Every short, meaningful domain name is already taken, but many of them come back when the owner stops renewing. A dropped name often keeps the backlinks, the rankings and some of the traffic its old website earned. For a startup that is a head start you cannot buy at a registrar.
Set the search parameters
In the Simple search, type the words that describe your product or niche into the Search box and leave Contains selected. Untick Allow dashes and Allow digits so only clean names come back. Under Extensions keep only .com, and under Listing Types untick Counter Offer. Tick Brandable if you want short, pronounceable names rather than keyword names.

The Pattern mode of the search box takes wildcards, so get* finds every name that starts with "get" and *ly every name that ends in "ly".
Check the results
Look at Domain Authority and Citation Flow first, then at the age and the website age: a name that had a real website for years is worth more than one that only ever carried parked ads. A low DA or CF means the name needs more research before you spend money on it. The info icon opens the domain's page with its backlinks and anchor texts, and the Wayback Archive button shows what the old website looked like.

Narrow the list
Once the keyword search gives you a manageable list, add a minimum Open PageRank or Domain Authority, cap the price, or limit the length of the name. Click the star in front of a domain to keep it on your WatchList while you compare candidates.