How do you add mods to garrys mod

Basically, you go to the menu, you go to where it says "Addons", then you hover your cursor over the mod you want, then you click install, after all that, you go to the spawn menu by pressing "c" on your keyboard when you play by yourself in single player, then go to Addons in spawnlists, then click a group, then click a picture or model, then it will appear. Some various mods can cause lag though. Also another way to download mods is through the steam workshop all you have to do is open steam go to your library go in Garry's Mod go down to the workshop area and download I prefer go do it this way because most mods require for you to reboot Garry's mod