How does one become an e-learning trainer/consultant/instructor from scratch?

Think about it like you are the person taking that course or instruction. How would you want that to play out? Make it as simple as possible, make modules for each section and create questions at the end of the module to assure your learners are absorbing the information.

You will know if you are being too technical or in depth because students will come forward asking for an explanation as to what you mean. There will also be a large number who did not do well in the question area.

Part of that simplicity comes down to how basic your language is. Explain it in two or three sentences but mix it up a bit to hold their attention. Now, in order to get people interested, it would be best to already have a following so you have something to offer them.

As to the format, mixed media will help since by having different methods, they will not be as likely to become bored. Be sure your content is up-to-date and well-informed by talking to experts in the field. That alone is what will make this useful for your audience.