Hey, we've all been there. In other words, it's like an appetizer - you get to sample the goods before you fork over the bucks to buy the complete program. Alot of companies make demoware available hoping that you'll buy the whole program or game at the store.
Freeware is cool - no worries, it's free.
Once you download it, you don't owe anybody anything for using it. Shareware is based on the honor system. Programmers write these cool programs and make them available for download. Here's the catch - if you use the program more than once, then you should register and send the creator a check. The cost is usually under 50 bucks, often considerably less.