filter design steps and process
Your question is overly broad and fundamentally impossible to answer because one needs preparation and no one knows how prepared you are. 

Matlab and signal processing are 2 different things. It is used a lot by people who do signal processing but they are not the same.  Learning Matlab if you have some programming background and some linear algebra is not hard.  I’ve seen 60 year old die hard FORTRAN programming engineers pick it up in 2 weeks.  They understood the numerics and it was just a matter of reexpressing their knowledge.  

Using a tool you don’t know how to use on a problem you don’t understand is very difficult. Did I do it right? Is it the code? Is it the algorithm?  Often it will be both. 

FDTOOL is considered easy to use.  

The Understanding Digital Signal Processing by Lyons is recommended.

Look through the old posts on this sight, particularly those that are “frequent”.  

Some people learn in a line. Other people learn in a circle. They revisit concepts after learning new ones. Circles have no start and end. I think everyone is a bit of both.