Creating a wallet in Bitcoin is incredibly tricky. Depending on your need, there is various tools that will help you to reach your goal.

A Bitcoin wallet must do the following:

1. Generate addresses.
2. Recognize transactions spent to these addresses.
3. Detect transactions, those are spending from these addresses.
4. Show the history of the transactions involving this wallet.
5. Handle reorgs.
6. Handle conflicts.
7. Dynamically calculate transaction fees.
8. Build and sign transactions.
9. Broadcast transactions.

Doing all of this by yourself from scratch requires serious skills and experience. Luckily there are tools you can utilize.