My family is moving to the US because of my dad’s job. I have just completed secondary school and have my IGCSE results. Im not sure what I should do. I don’t think I can apply to a university since I haven’t done my A’Levels, so what options do I have? Any advice would be appreciated! 
You’ll provide your official IGCSE results to your new school. They’ll decide between placing you in 10th or 11th grade. In terms of college choices being placed in 10th grade is easier since it gives you time ro build your record, establish ECs, and know which teachers to ask a recommendation from. If you’re placed in 11th grade you’ll have little choice and will have to hit the ground running since at many universities they stop collecting grades at the end of 11th grade and only need your 12th grade schedule.
You can apply and get admitted to reputable but not necessarily competitive US colleges with just your igcse. At least one person I know was admitted in the last month with just his predicted results since he only takes his igcse in May. Given that this is already the end of March, your opportunities for applying and gaining admission for the fall is rapidly shrinking though.
One very reputable (and competitive) example that accepts igcse…http://www.iss.purdue.edu/Admission/intlEd.cfm
Unless you hate school, your best course of action is to finish high school in the US. That will give you the largest range of options for university (in the US, at least): more universities that would consider you for admission, more financing options (from scholarships to in-state tuition eligibility), and more majors that you can complete without remedial coursework.
I don’t know if you know this, but the high school curriculum in the US is much more flexible than in most other countries. Students can choose their courses independently of each other, at different levels of difficulty or progression (subject to scheduling constraints). For example, a student could be placed into an advanced math class and a first-year foreign language class.
That flexibility makes it comparatively easy for American high schools to absorb newcomers from different school systems. It’s nothing at all like trying to enter an IGCSE or A-level program part-way through.
Enjoy your adventure!