1) have bank account
2) create account on coinbase, android app preferred
3) do coinbase verification steps (send photo of your ID, do test withdrawel from bank, etc)
4) buy some bitcoin.
5) wait for transaction to finish, takes a couple days unless you pay the higher fees for a debit card buy.
6) install bitcoin wallet app
7) transfer your coinbase bitcoins to your app wallet address this is the most important step, if you don't do this and buy questionable stuff directly with your coinbase account you will get banned from coinbase.
8)spend your bitcoins