Google Tag Manager is a free way to manage all of the tracking code needed on your website.
Unless you are proficient with modifying WordPress Themes, is how to install Google Tag Manager in a WordPress site.
Step1: Create a Google Tag Manager Account
Step2: Now create a container, where you will store all the tags for your WordPress website.
Use the name of your website as the name of this container (You may have other containers in the future for
other websites). Choose “Web” for “Where to Use Container”.
Step3: Now go to the Admin section, and from the Container select “Create Container”.
Now your container is set up, open it and go to Admin.Now Click on the gear symbol next to “Install Google Tag Manager”.
This is the code snippet,now just copy the GTM Id and paste that in WordPress Plugin
To install Google Tag Manager,copy and paste that code snippet into WordPress.
If you are using a Purchased theme,then you might not want to edit your theme directly.Then you just modify your theme using a child theme. In both case, the process of pasting in the code snipped is similar.
Step4: Login to WordPress dashboard and navigate to Appearance > Editor.
Click on Theme Header file, this is the place where you need to add the code snippet
Testing Google Tag Manger is installed correctly or not using Tag Assistant
Now Test that Google Tag Manager is Correctly Installed in WordPress
Now use Tag Assistant (by Google) to make sure that Google Tag Manager is installed correctly.
Open the Chrome browser, and install Tag Assistant. Once Tag Assistant is installed, simply navigate to a page on your site, and click on the tag icon at the top of your browser. You should see a green tag labeled “Google Tag Manager”, indicating that GTM has been successfully installed.
That’s it now you can see that the Tag was Added Successfully.
If your not a developer and don’t want to edit the code and add those all stuff,Then there is way to make it simple by adding a plugin,visit this http://nectarspot.com/how-to-install-google-tag-manager-on-your-wordpress-using-plugin/ you can find how to setup google tag manager using plugin