Hey there Salance,
Installing texture packs on the mac is quite easy.
If you download a texture pack, you get a [blablabla].zip file.
Drag the file to the desktop.
Open up your finder, go to the library, go to application support, and then search for minecraft.
The minecraft folder has some folders in it, one is the texturepacks folder.
Drag the .zip file into the texturepack folder, and you are ready to go
Just start your minecraft, and select the texture pack.
! If the texture packs have a higher resolution than 32x32, you need to install a patcher.
If you have any more questions, feel free to write a PM to me
Greetings!