All they ask is you leave your computer on so that it can run a couple of times a week to analyze data. Seti will download automatically several work units to test your system to see how long it takes to analyze the data. At first the time to completion will be very long but as Seti gets a better idea of how long it take, the times will come down to a more reasonable number. You don't really have to do much with the setting unless you want to. The screensaver will run according to the preset preferences on your computer. If you want to change these you can. By default, Seti is designed to run only once it notices no activity after a set amount of time. If you want to change that we can help you to do so but if you only want it to run when you aren't using it then we can just leave it as is. Why leave it as the screensaver? Well, it can slow down your system when you are working. If you are not planning on using the computer for anything else but analyzing then we can tell you how to change the preferences so it runs all the time.
Credit is just a way to give a value to the work you have completed. It can't be used for anything and you can't buy anything with it. It is a means to show those that want to know a value of how much they have contributed to the project. For dedicated persons, there are groups people can join and as a team they can contribute to the teams total credit and use that to compete against others to see who can do the most in a day or total. But that is not required to participate in Seti, it is more for a person's own self enjoyment. How is credit determined or given. I can't give you an actual calculation on how much a work unit is, there are other here that can but it gets rather technical.
There are 2 types of work units. Multibeam (MB) and Astropulses (AP). MB tend to be shorter work units (minutes to hours depending on the complexity) and therefore less "credits" AP tend to take much longer to process (hours to days) and give higher credits. How does seti determine which to send to your computer. Again, Seti will send a series of work units to your computer and see how long it takes to process them. If Seti determines that your computer takes too long or if too many errors occur while processing then seti will either restrict or not send a certain type of work unit to your computer.
Since Seti has determine that you do not have a graphic card that it can use, I'm not going to go into GPU (graphic cards) and the different types of work units for those with you. ok? For now, Seti has downloaded several work units to your computer for processing and at least 1 has come back.
Each work unit is sent to 2 persons. The result of each person is compared against the other. If both results match, then both persons are granted credit. If they don't match, the work unit is sent to a 3rd person to analyze and then that result is compared against the first 2. This can go on for as many as 5 attempts. When they work unit is sent, a deadline is give. If only 1 person returns the results by the deadline then it will be sent to another with a new deadline. No credit will be given until there is a match between results. Sometimes your result may not match someone elses in which case no credit will be given.