To install Google Tag Manager on a landing page:
1. Copy the first code from GTM admin panel.
3. Once you are here, select "Add script" button.
4. Name your script, e.g. GTM, paste the above from Google Tag Manager and set your position to "Head". Next, set the page to both (landing page and conversion page) and save the changes.
5. In the next step, return to your Google Tag Manager account and copy the second part of the code that you added in a separate script (for example, GTM 2).
In this case, set it to "Body top", also on both pages. Then save the added script.
6. So, if you finished in the Landingi side, go back to the Google Tag Manager page and move to the added container. Now, you must submit & publish your GTM.
7. When you publish GTM, you can add your tags and monitor your stats.