How do I protect my idea before presenting to a large company?
First, while there are cases of companies "stealing" an idea and giving nothing to the inventor it is uncommon (as far as I know). The reason for this is that ideas tend to be plentiful. It is the execution which is where the hard work comes in (and the risk of loss of investment).

Second, if you want to protect your idea, then you need to know what protections are appropriate for your idea. Some things are patentable and some are not. Some are patentable in some locations and some are not. So contacting an attorney in your area is a good idea (it won't be free but for a few hundred dollars you can get some advice which could make all the difference for your future. Besides patents, you might consider having everyone present in the meeting at the company sign an NDA. Keep in mind, some people refuse to sign NDAs for philosophical reasons (if you want an NDA you should bring this up well before your meeting, do not surprise anyone with it).

You might also consider checking out Law.SE but it sounds to me like you really need a one-on-one with an attorney.

Being able to find simple, innovative solutions is a great skill to have. It sounds like you do need to have the right team around you (to provide the skills you are missing) but do not sell yourself short.