For a more advanced search in Gmail:
Move to the Search box with / (forward slash) and press Down Arrow, for suggestions based on recent searches. If you type keywords and then Down Arrow, it will give more relevant suggestions. Press Enter on one of the suggestions to perform the search.
If you want to find something more specific, move to the Search box with / (forward slash), press Tab, then press Enter for Search options. Tab through the different fields, adding the information that you are looking for. Eventually, you will get to a Search button, so press Enter and you are taken to the Search results.
If you want to get even more advanced, there are a set of search operators that you can use. For example, you can type has:youtube in the Search box and it will list all the email messages that have a Youtube video link within them.
Follow this link for a full list of search operators.
To get back to the Inbox, from the Search results, press G then I (Go to Inbox).
If you get stuck in the Search and you just want to get back to your list of email messages, press Escape.
Note: If you use a screen reader, you may need to switch the “virtual cursor” off so you can use these shortcuts. Press Insert (or Caps Lock) + Z in JAWS or Insert (or Caps Lock) + Space in NVDA and Narrator.
Microsoft Edge and Mozilla Firefox work the same as Google Chrome for Advanced Search in Gmail.