You can frequently find answers in Guides at the top of the forum when you have questions. See this one on how to create an account (a bank account is one form of a cash account):
You don’t synchronize Manager with your bank accounts, as in having real-time data pushed to you. That raises enormous security problems. Some banks allow you to export bank statements, which can be imported to Manager:
Of course, your bank doesn’t know what the transactions are for, in terms of which accounts they should be posted to. After importing, many of your transactions can be categorized to proper accounts using bank rules:
Remaining ones must be judged and categorized manually.