Bitcoin is a distributed network that is considered "pseudonymous," not "anonymous."
While there are steps you can take to make it harder to identify your transactions on the bitcoin network and add layers of privacy, bitcoin should not be considered completely private by default.
Every transaction on the bitcoin network is recorded in a public record called the "blockchain" that is visible to anyone in the world, showing bitcoin addresses, the balance of those addresses, and the interactions between addresses.
If your "real world" identity is linked to a bitcoin address, then some good guesses about your activity on the bitcoin network can be made by programs which monitor addresses and the interaction between addresses.
Bitcoin wallets that generate new addresses with each transaction can increase privacy, but it is not perfect.
There are also "mixing" services that will mix your bitcoin transaction with other transactions to add an additional layer of obfuscation to your bitcoin.
Future developments in the bitcoin protocol may offer additional privacy features.
