Percentages of equity with the company are assigned through agreement. There is no possible way someone could come and take over a percentage of a limited company (a hostile takeover) unless the major shareholder agrees or someone else with a percentage of equity sells their share of the business.
I heard you wanted to start your own business and you really do need to be comfortable with it all before you think about starting, by the sounds of it you have a long way to go. I've been looking into business on a personal scale for many years and I'm still going to finish my A-levels before I'm comfortable with everything.
I'd advise taking up a professional course of education if you're looking at starting a limited company with no current experience.