It will not automatically fill in the ProjectTitle in the demographics table for you. the idea of a relational db is that you have each piece of information once (Project Title) and just display it where you need it.
cainemart is talking about building the relationship between the two tables (on ProjectID) so that when you create queries or forms or reports, information like the ProjectTitle can come along into your resulting display. do you know about queries and report Record Sources?
the gist of the answer for your original question is that you would build a form where for example you want to enter all the demographic details of people on a Project. The record source of the form would be your table ProjectInfo. within that form, you would have a subform based on your Demographic table, and plunk that subform into your main form. the two forms are then related with Master and Child designated as ProjectID. maybe you have never done this and don't 'get it' right now, but essentially you would be entering demographic info that pertains to a certain 'project'. since the master and child links are set up, whenever a user types in something in the 'demographics' subform, the data is entered into the Demographics table along with the ProjectID of that project you are entering data for. you dont do this just by typing into a table. you do it with forms. well, you could do it by just typing into a table, but you have seen the results.
look up:
queries
forms
subforms
relationships
g