Some would know this why some wont
Mod simply means ehancing the game ability or stuffs..Below are the steps
1.You must have Img tools on your pc
2.Go to Gtaplace.com
3.Click on San andreas mods download the king of mod you want e.g Cars,Bike,Plane..
4.After the download,go to your san andreas user files
5.locate 'gta3'
6.open gta3 with Img tool
7.You must know the kind of mod you download if it is car e.g Landstalker
8.In the img tool search for landstalker
9.After you have seen it left click it and replace it with the mod you download
10.For example Landstalker.dff and landstalker.imd make sure you replace both
11.At the top of the img tool you should see some like Rebuild Archiev...
12.Click on Rebuild Archiev
NOTE: Make sure you replace both of them dff and imd any how it comes.After you download your mod you must extract it with a app some used Zip compresser the one i use is Winzip if you dont extract your mod you wont see any dff or imd
13.Open your Gta San Andreas..The car you modwill have changed For me I changed Clover to Ferrari.....If helpful dont forget to like