I'm not a designer and whenever I have to add an icon to a website or software that I'm creating, I'm relying on others to help me out.
One option that users have when it comes to icons that they want to use for their projects is to use icon packs. Many are freely available while some are paid or require you to attribute the icon in a specific way.
Icons8 is an icon pack software for Windows and Macintosh that is available as a free and paid version. All icons can be used for free but if you don't purchase a license, you are required to link to the Icons8 website on pages or in programs that you use the icons in.
Different licenses are available that add other features such as access to vector icons, PSD files, or custom icons.
Once you have downloaded and installed the program on your system, you can start it up right away. Note that the download is quite large as Icons8 ships with all icons included.
While that means that it takes longer to download the 90+ Megabyte file, it means that you can use it without the need for an Internet connection while you do so.
The interface is packed with features. You can change the default filter -- all platforms and png 512 -- if you want, for instance by changing the size of icons or restricting the platform to Windows 8, iOS 7 or Android.
A search is available that you may make use of to find specific icons such as computer icons, cars or business icons. It works reasonably well but you will notice that icons that do not match the search are displayed as well. The reason here is that the program is matching what you have entered to icon descriptions. A search for car displays cargo ships, poker cards, carrots and cars among other things.
The left side of the interface displays icon groups that you can select to only display icons filled in that group.
A right-click on any icon displays a context menu with options to save the icon to the local system, to copy it, and to find similar icons.
As far as linking requirements are concerned, you find information about that on this page. Basically, it is required to put a link on any page or in any program that the icons are being used in.
You can view all icons on the Icons8 website as well, and evne download it from there directly without installing the program first. That's useful to discover icons and check out what is being offered without having to download the 90 Megabyte file first.
Icons8 offers excellent value even for free users. While you have to link to the website to use icons in your projects, you can at any time buy a license to avoid having to do so. Licenses start at $149 though.
All in all a great service for free and paying users.