How can we get credit?

I’m a 21 year old female and my boyfriend is also 21 years old. Niether of us have any credit at all. Never had a car financed, never owned a credit card, nothing. I’m in college and working and he’s working. I’ll be in school for another three years before I graduate and we would like to buy our first house shortly after. So, therefore, we need credit.

We both applied for a credit card with First Premium Bank and we both got denied. I then tried for a Capital One Card and also got denied. I did some research online and found the Discover Student Credit Card and applied for that. They said I’ll hear back from them in 30 days.

First question: If I find a credit card that I get approved for and I end up getting approved by Discover, do I still have to take the Discover card or can I decline getting it?

Second question: What are some good first credit card for those with no credit at all (not just students)? Rewards would be good, no annual fee or hidden fees, etc.

Third question: I heard another way to build credit is to finance something. If my boyfriend wanted to finance an engagement ring and make monthly payments, how can he go about doing that?

Fourth question: How long does it take to build good credit? If we keep everything paid off, will be be able to buy a home in two or three years?