If you havent bought the bitcoin yet its true that the price you buy it at is locked in and the funds arent available for 5 days or so to send off coinbase to another wallet/recipient as
@hogan86 has described. With a credit card purchase of bitcoin the balance is immediately available, however coinbase does not do credit card purchases anymore. You can though, immediately "sell" the bitcoin back and transfer it into fiat on coinbase's accounts and hold your bitcoin in dollars until its available to be sent off coinbase after the 5 days or so ams you won't lose money on the off chance it tanks, you also won't gain any, its a crapshoot as has been described lol most of the time it wont tank 20% of its value in 5 days, but its a much more real possibility than other currency forms, ive been there lol it sucks
Another option is a bitcoin atm. You can go to one of these, use a credit card and purchase an ammount of bitcoin that you can immediately send as a payment as long as you have the address youre sending it to. These are all over now, a google maps search will show you where they are, even where i am in the middle of nowhere theres 2 or 3 at gas stations in a 15 min drive. Most at gas stations seem to take credit card only, not cash, with around a 1500 dollar limit a day. If you want the extra anonymity of cash there are locations where they take cash. I havent used one of these atms as of yet, just researching, you can watch some YouTube videos on bitcoin atms if this is a route you might like to take
If the purchase is for something not 100% legal in your country and youd prefer folks not being able to trace it on the off chance someone actually gives a shit about you ans what youre doing. Buy the bitcoin And send it to a personal wallet, preferably an encrypted, hardened wallet and then send the payment from there. As an extra precaution you can make the purchase/payment in a tor browser on your computer with an active vpn (virtual private network) that will scramble the origination of payments and activities away from your computer. You can even send your bitcoin through a laundry process for a small fee that rotates it through 5 or 6 or more transactions and sends it back to you or the recipient as "cleaned" When the govt or law is tracking bitcoin they get from a drug bust or some such thing, they go back 5 or 6 transactions at most, past that even if they trace it to you who cares you cant account for or be held responsible for where the dollar you put in a strippers g string goes after you spend it, same idea