There are only two individuals who can draft a treaty: heads of state and foreign ministers. When one of them composes a new treaty, s/he can which positions on any number of variables, s/he wanst to be permitted by the treaty, creating articles. As it is an executive action, in order to draft a treaty, players must access the executive actions page through the cabinet page. Note that a treaty can also have no articles and be role-play only: this is the standard option used to create alliances- since it is a feature not yet included in the game.
The same two persons can demand the ratification of a treaty, selecting it from the Treaties section. Since the ratification of an international act is binding for the entire nation, it require a supermajority of 2/3 of the legislature.
Any party can demand the withdraw from a treaty, and its request can pass with a simple majority of 1/2 of the legislature.