Is necessary to create a new table in this context? I have a table Template and another ProjectDescriptions. A template can have many ProjectDescriptions, so the tables are like this:
Template: id, title, etc
ProjectDescriptio: title, description, template_id, etc

In the backoffice there is a screen for the user to create new project descriptions for a specific template.
In the frontend there is a list that shows the project descriptions for a specific template. There is a combobox for the user to select the project description that he wants, the can associate more than one project description to a template. My doubt is how to store the selected project descriptions. Is necessary to create a new table?
If the same ProjectDescription can be used by multiple different Templates then you'll need a third table, as a linking table, for the many-to-many relationship between the two entities. Otherwise you'd be forced to store duplicate rows in ProjectDescription which is bad design from a Normalization standpoint.
The linking table would be simple and just store template_id and projectdescription_id, and the primary key would be a composite key on both those fields.