What will happen next after I complete my general ed classes after 2 years ?

Nothing happens unless you make it happen.  If you are at a community college, then you generally transfer to a 4-year school after 2 years IF you want to earn a bachelor's degree.  You can choose a major when you enter the 4-year school.  

You decide what you do next and take the appropriate action. Nothing "happens" automatically when you finish an AA in general education at a CC. If you want to major in something and get a bachelors degree, yes, you will need to apply to transfer to a university that offers a 4-year degree.  Your general studies classes at a CC are the foundation requirements for a 4-year degree,  not job training or a major.  

Yes, you can choose the major you want, provided that there is space at the university in that major.  Many popular majors may be full or "impacted."  That means that there is no room to add transfer students or existing students who what to change majors.

You need to meet with the transfer advisor at your current CC to discuss your options.   You do not have to get a bachelor's degree and you do not have to transfer immediately to a university.  If you don't already understand this, you need to meet with advisors at your college so that you do understand your options.  

An Associate degree in general studies is really only beneficial if you continue on to a university to complete your Bachelors degree. That is what it is designed for, to transfer

Yes, you can declare any major- as long as you have the GPA needed for that major.  Some majors, such as electrical engineering, can require a rather high GPA.  And you may find there are some prerequisite classes you need to take for the major.