Total RP 3 is available for download on Curseforge. There are two ways to install and update Total RP 3. The first and easy one is to use the Curseforge Client, a desktop application that will manage your add-ons folder for you. If you don't want to use the Curseforge Client you can install and update your add-ons manually.

Using Curseforge Client

Curseforge is one of the main repository of add-ons. They offer a free desktop app they call the Curseforge Client that you can download on this page.

If you have more than one World of Warcraft installed (for instance Retail and Classic), you can select the install folder you want to manage in the top right dropdown.

The Client will scan for existing add-ons on your installation. If it finds updates, they will be indicated by an update button. All you have to do is click this button to update the add-on. You can also click "Update All" at the top to update all your out of date addons.

Once the Curseforge Client is installed, you can use it to install new add-ons for you, either by browsing the built in repository of add-ons by clicking "Get More Addons".

Or by clicking the "Install" button while browsing on Curseforge website.

Manually

If you don't want to use the Curseforge Client, you can manually download a .zip archive of the latest version of Total RP 3 by clicking on the "Download" button on Total RP 3's Curseforge page.

Once the download is finished, you have to extract the .zip archive. You should get a couple of folders named totalRP3, totalRP3_Data, etc. containing several files and folders.

Now move those folders into your World of Warcraft/_retail_/Interface/AddOns/ folder (or World of Warcraft/_classic_/Interface/AddOns/ if you are installing the Classic version). If you have a previous version of Total RP 3 installed, you will have to replace the old ones.

When launching World of Warcraft, make sure that Total RP 3 and its modules are in the list of add-ons found by World of Warcraft by clicking on the add-ons button in the lower left corner. If you don't see the button, it means that you didn't move the folders correctly. Make sure you move each individual module folder, not the parent folder.

You may have to check the option "Load Out of Date Addons" if a patch for World of Warcraft was recently released and Total RP 3 hasn't been updated yet, but you may encounter issues caused by patch changes.

External resources

FAQ: Installing & Troubleshooting AddOns - Forums - World of Warcraft

WoWInterface - FAQ: Installing AddOns