I have an idea on my mind related to a feature on a mobile that can help someone in their life.
I am outside of the USA. How can I protect my idea and where can I register it so later no mobile company or other people can take it?
On your first point, you would typically apply for a patent in your home country first. Within the first year, you would then apply in other countries (such as the US) via Convention applications or alternatively via a PCT application. In this manner, you can protect your invention in whatever countries you deem worthwhile.
You should likely discuss this with a patent attorney in your country. Alternatively, your university may have a IP commercialisation arm which could help.
Your second and third points [edit: that have been edited out of the question as of topic] are off topic for this site (since we only deal with patents). Startups might be a good place to ask though.