Licensing can be complicated. Previous poster did a good job of explaining the usual Creative Commons licenses for artwork. I specialize in knowing software licenses.
The GNU General Public License (GPL) is a copyleft license, which means that it works like the CC-*-SA licenses. You must release derivative works under the same license (or in the case of GPLv3, you may also release it under the AGPLv3, discussed below). The GPL says that all who receive a licensed copy of the work have the freedom to use the program as desired, change the program as they wish (source code is required for this), distribute verbatim copies of the work, and distribute copies of their modified versions. These are the basics of free software, the idea that computer users should be free to do their computing as they wish, not as some other entity wishes. Free software has nothing to do with price. Keep than in mind if you ever see that term. Also, do not confuse free software and freeware. Freeware is nonfree (proprietary) software that you can get at no cost (gratis, as we say).
The GNU Affero General Public License (AGPL) is also a copyleft license. Version 3 is identical to the GPLv3 in every way, except with one additional clause: if the software is interacted with over a computer network, that interface must expose the corresponding source to the software in use, so that all users could modify it and put up their own version if they so desired. This is the license I use on all of my original software.
The Expat license (commonly called the MIT license or X11 license) is a permissive license. Essentially, it says you are allowed to do whatever you want except claim warranty from the copyright holder. I do not recommend this license, only because it uses some unclear language such as "significant portions" of the software, which has no legal definition.
The ISC license is a permissive license identical to the Expat license, but with clearer language. If you want to use a permissive license, I recommend this one.
Licensing can be complicated. Previous poster did a good job of explaining the usual Creative Commons licenses for artwork. I specialize in knowing software licenses.
The GNU General Public License (GPL) is a copyleft license, which means that it works like the CC-*-SA licenses. You must release derivative works under the same license (or in the case of GPLv3, you may also release it under the AGPLv3, discussed below). The GPL says that all who receive a licensed copy of the work have the freedom to use the program as desired, change the program as they wish (source code is required for this), distribute verbatim copies of the work, and distribute copies of their modified versions. These are the basics of free software, the idea that computer users should be free to do their computing as they wish, not as some other entity wishes. Free software has nothing to do with price. Keep than in mind if you ever see that term. Also, do not confuse free software and freeware. Freeware is nonfree (proprietary) software that you can get at no cost (gratis, as we say).
The GNU Affero General Public License (AGPL) is also a copyleft license. Version 3 is identical to the GPLv3 in every way, except with one additional clause: if the software is interacted with over a computer network, that interface must expose the corresponding source to the software in use, so that all users could modify it and put up their own version if they so desired. This is the license I use on all of my original software.
The Expat license (commonly called the MIT license or X11 license) is a permissive license. Essentially, it says you are allowed to do whatever you want except claim warranty from the copyright holder. I do not recommend this license, only because it uses some unclear language such as "significant portions" of the software, which has no legal definition.
The ISC license is a permissive license identical to the Expat license, but with clearer language. If you want to use a permissive license, I recommend this one.
There are many more free software licenses. You can read about all the notable ones here: https://www.gnu.org/licenses/license-list.html
If you have any questions, just let me know. Happy hacking.