Hi Eleanor Duddy
You've hit on a huge subject here.
Firstly, the Perform Search button already has its 'mini screen' around it. Everything in this screenshot can be used to perform a customised search. Otherwise, when you click on 'Perform Search' with a TM open in the window below it, it will display the first page of the entire TM as there were no search parameters entered.
This is described in more detail in the SDL Trados Studio 2019 Help, for example here:
Searching and filtering TMs
You can search for words and also set up, use and save Filters that are created via the top line above and the dialog to the right that appears as a pop-out window with parameters you can select once you've given it a name. You can also use the above two together.
Here is the main topic in the Online Documentation:
There are loads more pages available on different aspects of the subject.
You can also perform batch edits and batch deletes on a TM. The introductory page is here:
Batch editing and batch deleting TUs
If you're not using Studio 2019 yet, documentation for all the other versions and all the other SDL software such as MultiTerm, is available here:
You select the version you require by clicking on the dropdown arrow to the right of the category heading.
There's lots of information out there. Much more than what I've given you above...
I hope this helps,
All the best,