When you create a project, you will be asked to define your website and the page you want to optimize (ie. the checkout page of an eCommerce website, or the pricing page of a SaaS website). Convertize filters the tactics from the library accordingly, and only shows you the ones that can be applied to the specific page you want to optimize.
So, if you have an eCommerce website and you decided to optimize the checkout page, the library only shows your tactics that are applicable to this specific page. You can further filter tactics yourself, for example by selecting the degree of ease of implementation or level of impact.
Please note that when you select a tactic and click apply, it will not be implemented by itself. For this, you will have to use the tool provided by Convertize in the Editing room to make the changes.