Shareware distribution gives users a chance to try software before buying it. If you try a Shareware program and continue using it after a reasonable evaluation period, you are expected to register.
Individual programs differ on details.
Some request registration while others require it, some specify a maximum trial period. With registration, you get anything from the simple right to continue using the software to an updated program with printed manual. Copyright laws apply to both Shareware and commercial software, and the copyright holder retains all rights, with a few specific exceptions as stated below. Shareware authors are accomplished programmers, just like commercial authors, and the programs are of comparable quality. The main difference is in the method of distribution.