setting up systems can mean a lot to different people. to me it means getting things set up in advance for repeatable processes. I can tell by your profile that you want to have buy and hold.
If you are buying houses that need a rehab that means you have a standard set of materials that you use. When you are looking at a house you don't want to have to go pick out tile, paint, flooring, faucets for that one house. You want to know what you typically use going into it so you know what things cost and you can quickly order/buy those material because you already have a part list you have used several times.
When you go to rent it, you already have your criteria in place. You have used it on your past rentals and it is the same everytime.
When you find a prospect, you go to the tenant screening company you already use. You know the format they give you the results, you don't have to ask questions because you 've used them several times and you have already worked out all those questions.
When you go to sign a lease you have that already prepared and it is just like every other one you've done. You know how to explain some of the clauses if they have questions.
You know how you are going to accept payment already, you have the forms ready if you are going to do a draft from their account etc. the tenant feels like you are a pro because you seem to know what you are doing.
When they are late with rent, you already have a late notice ready and you know how to file eviction because you prepared for that event.
When they move out you have your move out process worked up already, you can quickly get make ready done and ready to rent again.
When the AC breaks you already have a repair guy in your rolodex and you can contact them to get them out their with minimal effort from you.
For your finances you have a method to track expenses, organize receipts etc etc and you can easily get ready for tax time when that comes.
Basically the first time you do any of these it will be tough. The key is to take good notes, learn from mistakes and set up the process for the next time. You will have enough to do rehabbing houses or making offers on your next house that you don't have time to figure out things that you are know are coming such as tenant move out or figuring out how to take their payment. Don't reinvent the wheel every time for repeatable things.
Become efficient, make it repeatable, treat it like a business.