Hi @Eitan Dadda , welcome to the REI world!
1. How can I find a market to invest in?
This is going to depend largely on WHY you are investing. Coastal Cities tend to be better for appreciation but often require more $$$ money to get started. Other areas are better for cash-flow (Midwest - Cleveland, Cincinnati, Indy, Kansas City, Columbus etc) and require less $$$ to get started. Of course we all want both appreciation AND cashflow, and some cities will provide a little of both, but I'd pick which metric is most important to you and use that to help you make your decision.
Ok you've narrowed it down to cashflow or appreciation, now which city? Do your research, but there is no right answer, eventually you will have to pick a market and go with it.
2. How to search for a property? should I buy a house that's need a full rehab? or a partial rehab?
After you find your market, find a good investor friendly agent that can help you find your property. BiggerPockets is a great place to find agents who can help.
3. How can I check if the neighborhood is any good?
Lean on your agent here. They will be experts in whatever city you decide on and should be able to help you out. You can also just do some googling and read forum posts about your market, chances are somebody has created some type of guide that can at least give you a starting point for which areas to avoid.
4. If I live out of the state how can I find a good real estate agent? a reliable contractor?
BiggerPockets! Don't just reach out to one agent. Interview at least 3 and come ready with good questions. Picking the right agent will not only help you find your first property, but potentially your first 5, 10, 20 etc... If you are investing locally I would highly recommend attending meetups, there will be plenty of agents there that you can connect with.
You are asking great questions. Continue asking questions and learning. Just know that there will come a point where you will have to jump in before you feel completely ready, before every question is answered and that is ok. You will never have all the answers and you will learn 10x more by buying your first property. I hope this was helpful, and best of luck on your investing journey!