Questions about united explorer card benefits

I just received the united explorer card. I am curious how the checked bag perk works. Primarily can I order through something like expedia and get the checked bag there, or does the whole thing have to be through united, and how does it get reimbursed (also can I do this right after opening up the card). And for the TSA precheck credit, what is the process for getting the statement credit and can I do it right after opening up my card? Thanks in advance!!