In order to use Bitcoin, you first need to install a Bitcoin wallet on your mobile phone or computer. A wallet is a piece of software that manages Bitcoin private keys and allows you to send and receive Bitcoin. When you set up a Bitcoin wallet, you will have your own Bitcoin address which you can share with your friends and others with whom you want to transact. You can have as many Bitcoin addresses as you like.
Once you have some BTC, you can trade it on a cryptocurrency exchange, send it to your friends or use it to buy goods from stores that accept Bitcoin. Alternatively, you could just hold it for a long period of time and hope that it becomes more valuable in the future.