For the "dff" folder:
-Open IMG Tool
-Open IMG
-Search "gta3.img" (Usually found in Android/data/com.rockstargames.gtasa/files/texdb/here)
-Select "gta3.img"
-Click the three dots in the top right corner
-Click "Add files with replace"
-Find and Open the "dff" folder
-Click "All" then "Select"
-Wait
-Click the three dots in the top right corner again, then Rebuild (Optional)
-Finished

For the "Uncompressed 32bpp" folder:
-Open TXD Tool
-Click the folder icon in the bottom corner
-Search for "gta3.txt" (Usually found in Android/data/com.rockstargames.gtasa/files/texdb/gta3/here)
-Select "gta3.txt"
-Click the plus icon in the bottom corner
-Click "From Images" then "Uncompressed 32bpp"
-Look for the "Uncompressed 32bpp" folder then import everything in that folder (If you have found it, click on the box logo next to the check mark to select all the textures)
-Checklist

-Click OK
-Wait for all textures to be imported
-Finished



If you still don't understand, you can watch lots of videos on YouTube about how to install skins for GTA SA Android