This site answers tax related questions.
Actually, there are several non-tax related sub-forums on this site.
Which credit card is best to help with credit build up?
There's no single right answer. Basically, any credit card you can get, that you use moderately and pay on time. Don't charge more than 25% of your limit, and pay in full every month if you can. If you can, get a card with no annual fee, even if it doesn't have rewards or perks. If you are just starting out or have poor credit and need to rebuild, you may find that the fees on a rewards card are more than the rewards.
If you sign up for the "Turbo" app, which gives you credit score info, Turbotax will offer you some credit cards that may work for you. There are other financial web sites that offer lists of credit cards with different terms, most of those sites are probably compensated by the credit card issuers so take everything with a grain of salt.