How to Send/Receive Email with Thunderbird ver.115
This page explains the steps to send and receive email with Thunderbird 115.12.2 for Windows.
How to Receive
Receive
Click the 
icon in the upper left-hand side of the window.
How to Send
New Message
Click メッセージ作成 (= New Message).
Send
A window for creating a new email message will appear. After entering the address, subject and the main body, click 送信 (= Send).
If you are sending a test mail, enter your email address in the address field and send it to yourself.
If you successfully receive the test mail, your setup is done.