Here is the way to Skip mission of GTA San Andreas PC Game just in simple easy steps.

1. First Download and Install – WinRAR
2. Go to this page – 100% Savegame + Mission wise Savegame and download Mission wise savegame file.
3. Now Right click on GTA SA All Missions Game Save.rar ,then click on extract here.
4. Go inside the folder – GTA SA All Missions Game Save,then select any particular mission or last mission (100% savegame) ,then right click on that particular mission and click on extract here. Copy that savefile (file like this) – GTASAsf3.b 
5. Now paste it at this location – C:\Users\your username\Documents\GTA San Andreas User Files. Note: Before copying the save files, you can keep your old files to the safer location
6. Now replace the file if any file already exists.
7. Now restart your GTA San Andreas PC game, then select load game option and click on recent added savegame
8. All done, Enjoy.

By using this method, you can skip any particular mission or Skip all /any missions of GTA San Andreas, by simply putting the savegame file of GTA San Andreas at the savegame location.

if you are not understanding how to do it, you can watch the below video.