Help with designing a How-To for my android application

I am freelancer and is making a android application and I need to show a How-To guide to users, helping them how this application works.
Using this application users can book tickets to various buses our company provides for travelling.
It will be something like:

• Register your phone number
• fill out search
• select the bus you need
• click Book
• get a confirmation call back and text message

Please help me out to start, any suggestion is welcome. Also I would need some free icons or images for illustration, if you have any links please mention it. Thanks

Great design resource

100 Things Every Designer Needs to Know About People (Voices That Matter) Submitted March 03, 2017 at 10:04AM by rtvuser http://ift.tt/2llCeSD