In my opinion you need to know if you want a revolver or a semi automatic. And then you should understand the differences in the operation of each:
SA- Single Action- you must pull the hammer back each time with your thumb and then pull the trigger to fire.
DA-Double Action- pulling the trigger pulls the hammer back and then fires, all in one long, smooth pull. You may also pull the hammer back manualy like a SA, and then a light trigger pull releases it.
Striker Fired- All rounds are the same long steady pull.
Glocks,Springfield XD, Smith and Wesson M&P and many more.
DA/SA- Double Action/Single Action- First round fired is a long steady pull, all subsequent rounds are light.
Sig Sauer, Berettas,CZ and many more.
SA- Single Action- All rounds are the same light pull.
Colt 1911, Kimbers,Para-Ordnance and many more.
DAO- Double Action Only- All rounds are longer steady pull. Similar to Striker fired in operation.
Many manufacturers make these.
That's the abbreviated definitions, a little research should make it clearer.