I don’t think Warframes are really mechs, more biomechanical constructs. But there is a lot of modding that goes on in Warframe. As in customization of your characters, not Skyrim-levels of modding. It’s all in-game.
Modding is quite simple. You get mods as loot. You find a lot of mods on the ground, but some are mission rewards and some are… Dug up from the ground in Excavation missions. They come in three flavors, bronze, silver and gold, but these are rarity, not how good they are. Vitality for example ups your health but is a bronze mod. Continuity increases the duration of your abilities, and is gold.
The biggest problem though is that, by default, you don’t have much capacity. Your total mod capacity on your Warframe is [MR level] + [Warframe level] + [Aura mod capacity]. For me, using Volt, this works out as an MR of 5, a level 30 Warframe, plus a maximum rank Steel Charge aura mod which gives 18 extra capacity, giving me a total of 53. Most aura mods though only give 14 extra capacity, so a Warframe has anywhere between 30 and about 70 depending on your MR rank. Melee weapons have Stances that work in the same way aura mods do, but primary and secondary weapons only have the standard 30 capacity.
Sounds somewhat reasonable, until you realise that standard mods cost quite a lot. Almost everyone uses Intensify, which increases the strength of your abilities. It needs 11 free spaces at max rank. Then there’s Streamline, which is required to reduce the energy costs of abilities, and that needs 9 free spaces, again at max rank. I use Vigor too, which gives me 120% shields and health, it needs 11 free slots to be used. That’s 31 slots already taken by three basic mods.
Of course, it’s not that cut and dry. Every mod has a polarity, and some slots in your weapons and warframes also have polarities. Mods placed in slots with matching polarities will have their cost cut in half, so that Streamline I mentioned earlier will only cost 5 rather than 11. But that’s assuming that you 1. have the right polarities in a mod slot and 2. you have any mod slots with polarities in the first place. Most Warframes come with one or two maximum polarity slots, and most weapons come with none. My MK1-Braton didn’t come with one. Neither did my Braton Prime, annoyingly.
Now, there are ways to increase mod capacity further. The first way is to get either an Orokin Catalyst or an Orokin Reactor. Catalysts (blue, shiny potato things) double the capacity of weapons, Reactors (gold, shiny potato things) double the capacity of Warframes, Archwings and Companions. This is a flat double, so the game calculates your total mod capacity THEN doubles it THEN adds your MR (so I can get about 78 on Volt if I put one on him). This is all fine and good, but Orokin Reactors and Calatysts are not common items, they only appear rarely as alert rewards, or in Tactical Missions (which are semi-random 3-4 part missions) or occasionally as login rewards and other rare, random stuff. Or you can buy them with platinum. Either way, you need to save your potatoes for your most useful and all-round weapons.
The matching polarity system also does a lot to cut down on capacity costs, but it’s not great if you don’t have any polarity slots on your belongings. That’s where Forma come in. Forma are weird jigsaw-shaped things that are made from blueprints you can find in relics, or as daily rewards, or from Ludi on Ceres during some invasions. With a Forma, you can add a new polarity slot of your choice to your object of choice. So I can add a V (Madurai) polarity to, for example, Trinity, to get that half cost. But in doing so, I have to reset Trinity’s level to 0 and get her all the way back to level 30. Sometimes it’s not a problem, especially with secondary weapons (since all experience you get is shared between all your items).
Forma are also quite expensive to make and take 24 hours to finish building, so it’s not exactly easy.
That being said though, it gives people a reason to level up their mastery ranks. At level 1, that one extra capacity doesn’t mean much, but a MR17 player can put a max rank Serration on their brand new unranked gun, and still have it deal damage before it’s even leveled up at all. There’s also a reason to streamline your builds, to make them more effective rather than just throw everything on them. You can save the messing around until you get yourself an aura mod or a catalyst or whatever.
Plus, once you HAVE forma’d and catalyzed/reactored your stuff, you end up running out of mod slots. And the more leftover capacity you have, the more energy you start with when you start a mission.
Still, it’s a very bumpy ride for newbies, no matter what.