Need some help wondering how to add .ass subtittle files to mkv files.

First, download this. http://www.bunkus.org/videotools/mkvtoolnix/win32/mkvtoolnix-unicode-4.5.0-setup.exe
Install it. Shortcut on desktop? Sure, if you want.
Look for mmg in C:\Program Files (x86)\MKVtoolnix or wherever. Alternately, if you agreed to the shortcut on desktop, open up mkvmerge GUI.
From there, where it says Input Files: click "Add". Add the video file, audio file (if video came with audio, it'll automatically add it), and the subtitles. Feel free to click on the the files you just added to change "Track name" or "Language". "Default track" just makes it turned on by default, so that's generally a yes.
Then go and click "Browse" to select the location/name you wanna name your newly muxed file.

Heres the extra stuff... I'll put it in spoilers =O
If it's a script you've created and stylized on your own, click on the "attachments" tab. Click add and select the fonts you used. C:\Windows\Fonts or wherever your PC stores it oO.

Chapters... well I'll just explain it anyways.
Go to the "Chaptor editor" tab and then from the top, click chapter creator and "new chapters". Click "add chapter". Click on what you just created. Start and End times are self-explanatory. I would go by frames and then find the times they correspond to. Do note that just because you said time 22:45:32542, it doesn't mean it'll skip to that exact point when you want it to. Trial and error is a part of it (as well as your computers speed. A really slow pc means it'll probably skip past that time cause it sucks.) When done, go up and click "save as" and save the chapter somewhere... Then go to global, "browse" for the file you just saved, and select it.

From there, "Start muxing" or "Add to job queue" if you plan on creating more files. If the latter, When you queued up all your muxing jobs, go to "Muxing" at the top, "manage jobs", "start".

Open up your file and enjoy :)