Step 1 : Login into your account and open the tasks module
Step 2: Select the task that you want to add a dependency for, a window with all the task details appears as soon as you select it
Step 3: Scroll down until you find the dependencies field in it
Step 4 : Add the reason for dependency, for instance it could be blocked by another task
Step 5: Tie it to the relevant task that is causing the dependency
Step 6: Go ahead and highlight it as a blocked task by clicking on the ellipsis button and selecting the block option
Step 7 : Now that particular task would be highlighted as "blocked"