Creating Task Manager for Client Portal
You could create a "Matrix Block" and make 3 type of blocks in there:
Discovery task, Website task and Assets task. If you give these blocks the fields they should need they just add whatever block they need and fill it in the way they like. You can loop over these blocks so they get displayed.

They can be filled in differently for every "Client Portal"

You can find more info about matrix blocks here:
https://craftcms.com/docs/matrix-fields

The Craft CMS Documentation is really good especially if you are just starting its really helpfull as it got all the basics and even more you need to build a website with Craft.

There is also a "Craft CMS Slack" where alot of developers discuss craft and ask questions daily so you can have a more direct explanation and probably a faster response. 

https://craftcms.com/community#slack