Hello, this is my first thread and I'm not sure if this was the right section to start. 
Okay.. So I'm 19yo Male with 79kg weight and 178cm of height. I started to working out since the past 2 weeks and I need some advice from you guys.

I gained about 25kg of weight after I graduated from secondary school so I think that I need to work out before I start my college life and now I working out to loss weight at the same time I also want to gain muscle.

Since you are new to this it is possible to do both lose weight and gain muscle. After a while, you will need to choose either 1. Do a little research on 'newbie muslce gains'

Since the past 2 weeks I already loss 4kg as the result of working out but I have one problem that I feel I'm getting weak day by day. Is this because I'm tired or It because of the way I eat? I go to the gym six day a week (Monday - Saturday) and I'm not doing so much. Just 3 type of exercise each day with 3 set (6-10 reps). I just spent 2 hours at the gym. I start workout around 7:30PM and finish on 9:30PM.

Here my meal plan also what I eat in a week, (I don't eat all that I listed at the same day, I listed what I eat in a week)

For Breakfast: cereal+milk, toasted bread+jam, 2-3 boiled egg, fruit
For Lunch: rice, chicken breast, steam fish, vegetables, soup
For Dinner/Pre-workout: rice, vegetable, cereal+milk, fruit
Post-workout: Milk, bread, banana

Try to do some research on Macros and Calorie Counting. Also, do some research on some proven workout programs and pick one. Follow them religiously until you see progress and tweak them later once you fully understand what you need to do to achieve certain goals.

Another problem that I feel my left hand is weakest than my right hand. I can lift with my right hand but with my left hand I can't. Should I train my left hand first? or should I carry a light weight for both hand and focus on the right position/form first?

Study and practice the correct form, light weights for both hands for any exercise  

Also should I take any supplement? vitamin pills something like that? 

Depends on your overall food intake.

I'm thinking to start taking a protein shake but I don't know which type/brand of protein shake suitable for my age also my goals (loss weight & gain muscle). Need some recommendation. Thanks

Figure out your macros and overall food intake before adding supplement to the mix