The crochet design process is how things go from an idea in your head to something that can be shared with the world. Every designer is different, but I believe the basic steps are the same.
You have this great idea, now you have to put it on paper. Even if you think you can't draw, you have to try! The sketch is your base. It reminds you of where you are going. Use color to highlight certain areas or to make the sketch more complete.
How big will it be? Write down how long, how wide, how tall - use arrows if necessary. What weight of yarn will work best? What stitch pattern? The sketch is now becoming your blueprint for the design, so add as many details as possible. Remember, if you are planning to use this for a submission, you may not see it for a long time. You will need as many details as possible not only to impress your idea on an editor, but also to jog your own memory when the time comes to make it!
Now pick up the yarn and a hook and play with your chosen stitch pattern. Practice increases and decreases in pattern and see how it looks. You many decide at this point that a different stitch pattern or different weight yarn would work better. Change hook sizes until you get the look you want. Be sure to write down the hook size you settle on and any other changes in the notes.
You may also want to block your swatch to see how it will stretch. This is a good time to measure your gauge as well.
Go ahead and make it! Be sure to write down notes to yourself, such as how many stitches you chained, how many repeats, how many stitches per row, etc. Sometimes I will write "started 2nd skein here" and sometimes I will simply save the wrappers with the project to keep track of the amount of yarn. Keep in mind that you will be using these notes to write your pattern in a format the rest of the world can understand!
There are templates available for this stage. Some publishers have their own submission forms that can also be used as a template. Either way, this is the point where you take all those notes to the computer and start typing your design pattern. This is also the point where you will learn how strong or weak your note taking was. That's why it is best to also have your finished project with you to refer to if needed.
Please keep in mind that this is a very basic overview of the crochet design process. There are entire courses dedicated to the topic that cover all the details.