Most projects aren’t just a list of completely independent tasks. Usually a project has some tasks that can’t start until other tasks have finished. In Project Web App, creating this kind of a relationship between tasks is called “linking” the tasks.
Tip: Project Professional enables you to link tasks in more detailed ways. For example you might want to link a task so that there is some overlap between the finish and start dates, or you might want to link tasks that are in completely separate projects. For more information, see Open a project in Microsoft Project, Link tasks in a project, and Link projects.
To link tasks in Project Web App, simply select the tasks you want to link, and then press Ctrl+F2, or click Link Tasks in the Editing group on the Task tab.
Tip: Project not currently open for editing? Click Projects on the Quick Launch, click the name of your project in the list on the Project Center, and then, on the Project tab or the Task tab, click Edit.
The order in which the selected tasks are linked depends on how you selected them:
To link tasks in a specific order, press Ctrl and then click each individual task in the order that you want them linked. Then press Ctrl+F2, or click Link Tasks in the Editing group on the Task tab.
To link consecutive tasks in the order that they are listed in your project, click a task, press Shift, and then click another task. The two tasks that you clicked, and all tasks that fall between them in the list, are selected. You can also click the row header and drag up or down to select consecutive tasks for linking. Then press Ctrl+F2, or click Link Tasks in the Editing group on the Task tab.
If you no longer want your tasks linked, you can remove a link at any time. To remove task links, select the tasks that you no longer want linked, and then press Ctrl+Shift+F2, or click Unlink Tasks in the Editing group on the Task tab.