In Multi-Project-Planner a project is defined by

• Short title
• Title. (Mandatory)
• Site.
• Color. (Mandatory)
• Starting week.
• Total amount of man days needed, if known.
• Activities.
• Relative constraints, which are the the predecessor and successor relationships between the activities.
• Critical Path.

This picture shows the activity schedule containing two projects. Each projects has a color of its own.

This is the same picture, where the 'green' project has been selected and the relative constrains are show. The red arrows indicate the critical path.

See here how to create a project.