Something like this?

DG105 is a sealant.
DG501 is an AIO - paint cleaner and sealant.

DG105 don't have much cleaning/polishing properties
DG501 can do a little cleaning/very mild defects removal

DG105 protection last a little longer
DG501 protection last quite decent also, but not as long as DG105

If you're looking for a sealant without any defects/contaminant removing capabilities - DG105
If you're looking for removing some contaminants/very mild defects while putting down a decent layer of protection as well - DG501

If you're undecided - GET BOTH cuz they're both great products and good value for money....hahahaha.....

I took this picture off the internet. I don't really know much about this, but compounding / polishing is normally the way to remove those spots. To my knowledge they happen due to the lack of paint protection, and/or the lack of car paint care, e.g failure to wash the car as often as required, but I stand to be corrected.

Looks like swirl marks plus water marks.
Need to clay first followed by compound with a cutting pad.

I actually asked the same question before too. Found it again! 
Hope it helps!

Clay is not very tough to use. Just make sure you have enough lubricant(eg: use ONR, Turtle Wax Rinse Free Wash & Wax, car shampoo,etc.) while claying. Apply gentle force when claying on the paint.

If you ask me where to get the clay, I would say lowyat Automotive Garage? Haha. There are people selling for 3M, Meguiars claybar.

jyan are ur paint looks similar to this? =P

From my experience, you can use wax to remove it, although a better solution is probably to clay and then polish, or clay and wax if you do not have polish.

lol i have that problem too XD but not too headache abt it. How i prevent this is, frequent wash(i using sonax shampoo), frequent as in more than twice per week. I cured it with permanon's hecta, then rinse thruly with water, lastly with finishing wax, e.g. meg's gold class liquid wax. with this said, i don clay or polish to solve these damn dirt.
am too lazy to clay xD with this extra step i would took me more than 2 hrs just to clay, damned the size of my pickup truck! lol. cleaner wax/sealant may do the job, never try it tho.

  I don't know where the black stains come from, but from my observation they seem to come from all the rubber parts / parts where there is double sided tape. hmm.gif. Aside from that it's probably from the environment / rain and etc. You can polish then wax without claying, but only if your car's surface is already free from embedded contaminants, otherwise you will probably be removing the stains while causing scratches / swirls to appear.

Washing alone will not help, or at least it won't from my experience. I have experienced the black stains on my car hood quite many times as well even with recent waxing, but the wax is cheap. What I'd do is to take SwirlX (my polish) and rub the hood after claying till the dirt is gone, then put a layer of wax. I have switched to a better wax (or sealant to be specific) though and I haven't experienced such a problem, for now.

To remove dirt film, this these either of these method.

1. Wash > Clay > Dry

Else

2. Wash > Clay > Dry > (Start) mild polisher (not compound !) < If can't only go slighting more aggressive polish.

Your image shown that the paintwork is lack of surface protection or surface being exposure to head/dry after rain

I have a solid white color car, I face this problem all the time. It is form by dirty water (rain) on panels that water run off very slow like hood or roof. If you let the stain sits for few weeks, it is quite hard to come off. Proper polish is the way to go. If you wash once a week, should be very easy to wash it off.

What he meant by "proper polish" is using the correct polish product + correct method to remove the stain. As they mentioned previously, start with a milder polish product. If it doesn't work, proceed to the next level of abrasive polish product.

pls share the product list you have now. (E.g Shampoo - what brand ...etc)

please consider searching this thread for questions that have already been answered if you're serious in maintaining your car.

there are plenty of Q&A done for watermark removals.

then there are also many repeated guidance on proper detailing steps and maintaining steps.
example:
detailing
wash > clay > wash again (my preference in getting rid of clay lube/products/me just being OCD etc) > dry > compound (if needed) > polish > glaze or IPA wipedowns (if needed) > coating (if preferred) > wax/sealant

weekly regular maintenance:
wash > dry > maintenance wax/topper such as meguiar's ultimate quik wax or sonax brilliant detailer or duragloss aquawax (or DG951 http://estore.duragloss.com.my/webapp/wcs/...isplayErrorView )

for proper washing, do use the 2 bucket (or 3 if you OCD) system, with grit guards
search in this thread/google it if you're not sure. got youtube guide too.

get plush microfiber cloths and/or drying towels if you don't have any proper ones.
if you're on a budget, consider getting from osren: http://www.osren.com/

amway pyramid scheme items? consider sell/donate/throw.

google: https://www.google.com/search?q=OCD&oq=OCD&..._sm=93&ie=UTF-8

http://en.wikipedia.org/wiki/Obsessive%E2%...ulsive_disorder

layman in detailing/examples: will rage even seeing 1 dust on car, see microfiber cloth dirty also will flip table.

never under estimate the product you have now. No matter how poor or bad you call it...i am sure it will work at certain level (else you won't buy it right ?  ) assume both product also so called not popular...and priced at RM15 and Rm25, do you think RM15 product will not work at all ?

Same time even you have/bought all the famous brand etc..at high price (due to import tax), do you think the product will work superb to a pair of hand which doesn't know how to 'use' them > no offence.

My advice is use what you HAVE NOW, MAXIMISE it....and KEEP IMPROVING your technique till you find the product limitation...
As for clay, its doesn't require special technique...what you need is CLEAN surface (mean WASH it before clay)...after that GLIDE the clay bar on the surface (A MUST TO MAKE SURE) you have enough lubricant (either clay lub/quick detailer or easiest way is make a spray bottle of CLEAN SHAMPOO)....