Following are the different web elements that you may be present on any web application which you will automate:
Edit box
Link
Buttons like submit, reset, back, finish, ok, etc
Image link
Image button
Text Area
Checkboxes
Radio buttons
List box
Combo Box
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You can check out the Selenium tutorial, and Selenium Interview Questions to prepare well for the testing that you may appear in the near future.
Check out this video to know more about Selenium concepts: