It depends on how many fish you have and what kind. If you have a whole tank of carnivores (a large sized tank) who feed at the top then I have heard that you can just press one cube of them to the glass at the top edge of the water, but if the number of fish you have eating them is smaller, you don't want to give them more than they will eat in one meal. It will foul your water.
You have to be careful with live or frozen foods as sometimes the freezing process does not kill all the bacteria in the food and can cause you problems down the line. That is why some of the aquarium keepers recommend the freeze-dried bloodworms as the only form to use. There are however some who say they have used the frozen type with no problem. The choice is yours. Just be careful not to overfeed. If you see that they are not eating anymore after a couple of minutes, remove the rest as they will leave them to make your water dirty and smelly as well as unsafe eventually.
Welcome to Fishlore. This a great site with a lot of people and they are very willing to help. It has been a great help to me to be here and I have met some of the finest people I have ever met online and off. It is my hope you will have as pleasant an experience as mine. If you haven't yet, I invite you to browse the many topics and posts. There is a real wealth of experience and knowledge from a lot of people in there as well as a lot of really beautiful pictures.
Rose