Any activity that shows up as a gray link on your main course page is invisible to your students. Even if you set an available from date, your students will not be able to access these activities unless you set them to show. There are three ways to set activities to show.
Click on an assignment name to open the activity editor. Click the show icon in the Settings panel, which looks like a closed eye. The icon will change to an open eye to indicate that students can see it. If you don't see the Settings panel, you may need to close the library by clicking the book icon.
From the Activity Editor
Scroll down to the unit where you need to hide/show an activity. Click the three dots icon (...) to the right of the activity to open the edit menu.
From your main course page
Select Hide or Show.
Click Activities and Due Dates on the left side of your course home.
From the Activities and Due Dates page
Click the checkbox in the Visible column to hide or show the item. When the box is checked, the assignment is visible to students.
Or, you can use the checkboxes at the far left of the page to select multiple assignments, then click Edit Selected Activities to change the visibility setting.