if there is no vacancy, but i wanted to apply a job in the company, what should i write the title of the cover letter?

so u mean it really doesn't matter whether to list out it is beginner,advanced,etc or not?

With regards to blazer, if it's for the big time MNCs and "Guai Los(foreigner)" interviewers not wearing a blazer is UNDER-DRESSED to them. (probably dependent on the position you're applying as well)

Actual Situation:-
( Do note that I was wearing a long sleeve shirt with a tie, and apparently that's not enough. )
* exchange of simple pleasantries *
Guai Lo: Well, usually during an interview I would be wearing a suit but it's "casual friday" .
            Besides, it appears that you're not formally dressed at well.
Myself  : Haha, well I believe that in Malaysia, wearing a suit(blazer) would be ill-advised due to the weather.
Guai Lo: That's no excuse. We're not having an interview on the hot sun. We are in air-conditioned room.
Myself  : * stun expression * I see. Thanks for the tip. I'll keep that in mind for any future meetups and interviews.

Fortunately, I still manage to get the job.

( Assuming it's hot in the meeting room, just tell the interviewer and ask whether he minds that you take out the blazer. (That itself is another plus-point for yourself in speaking your needs & getting comfortable).
Side note: Speaking of which, I just notice out of the 5 interviews I went, 3 of the interviewers were wearing suit/overcoat. That's more than 50% probability!!? So why do you want to give the edge to other candidates. Be different and stand out(professionally and not in a bad way).