Vendor qualification isn’t easy but it’s also not especially difficult as long as you’re an American citizen with no criminal history. Figuring out the paperwork is half the battle.

Being selected as a vendor, on the other hand...

Do you have any links where I could read about either topic?

As an SME, everything starts with the GSA - there’s a good overview at https://www.usa.gov/become-government-contractor

Past that, the hoops you'll need to jump through depend a lot on which department is handling procurement. If you look at defense-related contracts, you'll also have to go through personal clearance (which can be difficult by itself at higher levels).