Step 1. Open Mozilla Thunderbird

Step 2. In the left panel, you can see a list of your email accounts. Double click on Inbox. Or if its hidden, click on your email, and it will expand and show the inbox, trash list, etc.

Another option is to right click on the email and click on Get Messagess.

Thunderbird also automatically checks email every 5 to 10 minutes. It also automatically checks mail when you open the program.