As a beginner, your first week with fish, just take the same kitchen timer or wristwatch you use to time your water tests and go ahead and set it for 3 minutes. Then feed your fish small amounts (it doesn't take much to put in more than they can handle at one time and then just get a feel for the size pinches and how many it takes to get you to 3 minutes when you have to stop. It will often feel way too soon. The fish will often seem still quite hungry from your point of view, but stop at the 3 minutes. "How much the fish can consume in 2 to 3 minutes, once a day," is the best of the most general feeding advice we usually seen given to beginners here on TFF in my experience.
After you've used the timer for a week your feel for how to judge it will be much better and will keep improving if you occasional do a timing check on yourself and make sure you haven't let the amount creep up. And of course when you find you've accidently forgotten to feed them one day, just consider that to be fine and don't feed them at all that day. That's more realistic to what they get in the wild and will be better for them.
Let me repeat that this is -general- advice and as your experience as a fishkeeper grows (through reading or local tropical fish society conversations or other experiences) you will definately gain more details about feeding specific species in better ways if you have the time and inclination. Some very small fish can indeed benefit from very, very small feeding twice a day, but its not essential. All fish can benefit from variety of food choice if its done with knowledge of the species and of the food offered. Two popular foods need a bit of advice: live or frozen brine shrimp can be a nice "treat" but be aware that from a nutritional standpoint they are like "candy" and should only be fed very occasionally. Likewise, bloodworms are a very rich food and should be only sparingly offered or they can cause digestion problems. On the positive side, you will see good discussions here on TFF about feeding the occasional vegatables and these are a good and healthy occasional change too. You can find the food discussions easily and the members have a wealth of other infobits in them.
Good grief, I've gone on and I doubt you are reading this my now, lol, so I'll mercifully quit!