When initially entering the game, there will be the familiar server list of all the possible servers you can join. These are categorized on the left. There are 3 public server categories: Official, Community, and Modded. Click on the Modded tab to show a list of available modded servers that you can join. Likely, the names of the modded server will have info on what mods they use.
No, you do not need to install any special programs or such in order to play on modded servers. The regular Rust application already has everything you need to run a modded game.(Keep in mind these are the same people who made Gmod, so modding is nothing new to the devteam)
Are you absolutely sick of people building ladders onto your property? Wish that ladders were part of the building privilege system? Don’t want to spend the resources into making anti-ladder defenses? Then this mod is right for you! This mod basically changes ladders to follow the building privilege system, so in order to place a ladder (within a cupboard’s radius) one must have access to the cupboard. Otherwise, like foundations and other structures, ladders cannot be placed. This mod is great for those who are often raided by ladder-wielding looters.