Penn State. Find a local Penn Sate soils office, get test envelope $10, select type of vegetation to be seeded, sample dirt, send to lab. I've sent soil samples to Penn State and done them myself, Penn State much easier, less time and money.
For the penn state tests you don't even have to get the test envelope, you can just send in your soil in a ziplock bag labeled with the forms on their website. I did this last year results came back quickly once samples were sent.
I think the OP want to know how you do a soil test. I maybe wrong.
Here is how I do it. I take a small hand held shovel and dig down about 4 to 6 inches and dump it in a clean bucket. I get 5 samples from each plot.
I do all four corners and one from the center. After mixing altogether i place a small sample into a plastic zip lock bag and then I drop them off at Agway.
PSU kit has directions on the forms
Extension flyer came in the mail today. There are free soil fertility sessions coming up across the state. You can find some here. The one on the flyer I got isn't listed. https://extension.psu.edu/soil-fertility
Here is one of my samples from PSU. They give you a little more info and i did some research to see exactly what these other numbers are reflecting. Ill try to explain some of this, if you watch some videos on youtube of Ag Phd these guys do a good job of explaining things but ill try to give you the highlights from what I learned.
First Ph is obviously low and we put a lot of lime down to correct this. The ph being so low effects availability of the nutrients which can be seen if you look at potassium. It says my PPM is in optimal range but when you look at the % saturation of K at the bottom its 2.3%. this is the potassium that is actually available to the plant which should be in the 4-8% range. Its because the K is bound in the acidic soil.
Another thing to look at is CEC so this is how much holding capacity your soil has. If you multiply it by 10 it gives you an estimate of how much nitrogen your soil can hold so on this sample mine is 11.6 so the soil can hold about 116 pounds of nitrogen per acre. Important to think about when applying fertilizer so your not wasting money.
One thing that it doesn't have standard but is an option is organic matter. So your organic matter is a percentage and it will release some nutrients throughout the year. example for each 1% of organic matter it will release between 10-30# of nitrogen per acre. So if ur organic matter was 4% and say we used 20# released you would have 80# per acre of nitrogen available and if ur holding capacity was 116# you don't want to go putting down to much nitrogen fertilizer because it will be wasted. Also the organic matter will give you some phosphorus 4-7# per acre.
These are just some other things to think about when your looking at your soil tests to try to have an understanding of whats going on. Also they do recommend fertilizer for your plots you can see what they recommended for mine as i planted brassicas in the fall and will put soybeans in this spring. They give you the pounds per acre to be applied I always go through and calculate how many pounds of N-P-K i'm putting down based on the fertilizer i have available to make sure I'm meeting the plants needs.