Using SafeSearch is quite simple to setup and it only requires a couple of steps to activate the search content filter. To start, navigate on over to the Google preferences which you can find here. From this page, you need to modify a couple of settings. The first option you are presented with is the interface language filter. Be default, this setting should be set to your country's native language. It's best not to mess with this setting. Doing so could lead to a hassle of unreadable content, which can be quite a mess, unless you are fluent in many languages.
The second option is "Search Language". Again, leave this setting alone. By default, it should be set on "Search for pages written in any language".
The third option is what you are looking for. There are three main options: Use strict filtering (filter both explicit text and explicit images), Use moderate filtering (filter explicit images only), and Do not filter my results. Choose option one, Use strict filtering (filter both explicit text and explicit images).
You will also be presented with an option to "Lock safe search". This will prevent settings from being tampered with, and carry filtering settings to all browsers on your computer. If you wish to do this, click the text that says "Lock safe search", and login with your Google account. If you do not have a Google account, you can also create one on this same screen.
Although not necessary, they also recommend that you use Firefox as a browser. If you wish to try Firefox, you can get it here.