Your checking account is likely your most active financial account. Money flows through your checking account constantly: paychecks, refund checks, meal share cash, etc come in, and payments for credit card bills, rent, services, etc. go out. You need to have money in your main checking account all the time. Naturally, this is probably the first financial account you have.
A checking account is the money that a bank holds for you that is safe, secure, most easily accessible, and immediately available. Your checking account is insured by the FDIC for up to $250,000, which means that if the bank goes out of business and is unable to pay you back the money you had in your checking account with them, the FDIC will pay you the full amount as long as it is under $100,000 (and I highly suggest that you not keep anywhere near this amount in your checking account).
You can withdraw money from a checking account at any time by writing a check or withdrawing cash using a debit card.
Think of your checking account as cash in non-physical form. It is superior to cash since it is kept safe and saves you the trouble of carrying a large stash of paper with you all the time. Having a checking account also allows you to keep track of your expenses: every single transaction through your checking account is recorded by the bank and is view-able by you.
If you don’t already have a checking account, you need to open one with a bank or credit union. No excuse; this is a must.