How do i find items skins and stuff

[hilly]

is it randomly given to players or do you have to find it please tell me

[Suzaku]

It depends on what skins you're looking for, but some are in the Steam market, some in the Steam Workshop, some are in the in-game market for platinum, and some can be rewards for alerts. You should check the wiki for info on how to obtain a specific skin.

[dyra55]

Skins? Items?

You want to sell those on Steam Marketplace?

Too bad - it doesn't drop them

[Watermelons]

Skins in the ingame market, 90% of them you have to buy.

Sometimes they'll set up free or extremely credit cheap skins for players during community events, seasonal times, or other sort of things. In the case of events, you'd have to complete requirements to get said skins as rewards.

Helmets though, they do pop up in random Alert missions.

Oh and no, none of them drop in your Steam inventory. There are a few skins that were around during Steam sale events, like the Rubedo skins released during I believe last Christmas. Those you have to buy now though. They were 'craftable' in your Steam inventory through collection some ♥♥♥♥♥♥♥♥ then building them to get a random skin.

[Procrastinating Gamer]

The Warframe Wiki[warframe.wikia.com] lists where you can get everything. Most cosmetics can only be gotten through the Market for Platinum, everything that affects gameplay can be earned through other means.