If you're an avid Gmail user, one of the startling aspects of Gmail as experienced through the Mail app on the iPad isn't that you can easily access all your email, even that in folder or labels. It's not that you can easily star email messages, change their label/tag and re-assign them out of your inbox at will.
No, the startling thing is that the inability to DELETE email. If you setup your Gmail account using the Gmail Account wizard in the iPad Mail app, you will find yourself hunting for the little trashcan that symbolizes delete or send email to trash. It's not available. Instead, you are archiving messages. I don't know about you, but I don't want to archive the countless emails I get from solicitors…I want to delete it.
Fortunately, I know that the DELETE/TRASH button does exist since I can see it on another IMAP email account I have. A simple solution is to NOT use the GMAIL account setup wizard in the iPad settings. Instead, set up an OTHER email account and choose IMAP email account.
Once you've done that–also entering your username and password where appropriate–you'll see your Gmail account information appear…and when it's time to delete an email in your inbox, you will see the Trash icon instead of the archive box!
Another neat tip is that if you look at your inbox, you can swipe left above a message title, and a DELETE button will appear.
Let me know if this tip is helpful to you!