I have read some of the topics on getting a U.S passport/Visa. I have not found anything saying what all a person in Nigeria must have in order to try to apply for them.
I am very interested in trying to find out as much as possible from anyone wanting to give me information.
Such as documents he will need,money etc.
Is it easier to apply to come here to study or to visit?

I cannot help you answering your question, because there are different types of Passport/VISA you are applying for and varies fees to pay for whether you are single, married, engaged/to-be married, and/or have children/family that requires to apply separate Passport/VISA application per person.

You should make aware the fact that all spouse, family/relative, children and babies if you plan them to travel with you that are required to apply for passport/VISA each person per application separately. You also pay separate fees for each Passport/VISA application for your spouse, family/relative, children/baby individually. All of them are required to be presented for Passport/VISA interview appointment in order to get fingerprinting and/or biometrics if grant passport/visa.

Check out existing topic you will find below:

How can someone living abroad obtain the new E-passport?
https://www.nairaland.com/nigeria/topic-93255.0.html

The following official US Passport/VISA sites at below:

If you are US resident (fully US citizenship) to find where to apply for a Passport nationwide, see this link of the Passport Acceptance Facility Search Page at below:

http://iafdb.travel.state.gov/

How to apply in person for a Passport link at below:
http://travel.state.gov/passport/get/first/first_830.html

How to get a VISA for immigrants (non-US citizens) link at below:
http://travel.state.gov/visa/immigrants/info/info_1339.html

You need to know which type of VISA you want to apply for.

The following official Nigeria Passport/VISA site from the US travel's external link at below:

If you are Nigeria resident (fully Nigeria citizenship) to find where to apply for a Passport/VISA, see this link of the Nigeria Embassy contact information at below:

http://www.immigration.gov.ng/index2.htm

If you plan to invite Nigeria person come to the US, then following needs at below:

Nigeria person must apply himself/herself on Nigeria E-passport or E-visa with your letter of invitation (sponsorship authorization letter or guarantorship letter), your copies of 3 first-page valid passport, your proof of financial support via fax document, printed PDF document or mailing to bring them along with his/her proof of citizenship, bank statement/employment paystubs, and credible supporting documents at Passport/VISA interview appointment. (Email attachment are not acceptable). Nigeria person must pay the passport/VISA fee through Embassy-approved banks prior to the passport/VISA interview appointment due.

I recommend for Nigeria person going to American Embassy in Abuja for US Passport/VISA request better than in Lagos.

Nigeria Embassy will not ACCEPT paper Passport/VISA form, they prefer electronic Passport/VISA that will generate the bar-coded printing in the quality of anti-fraud Passport/VISA application improvement.

He is a single person. It will be just him alone. He is from Benin city.
Is it easier for him to come here to study or to just visit?
What other credible supporting documents? How much income does a person have to get in order for most Nigerians to get approved?How much can this visa/passport fee be?
Please let me know anything else anyone can. Has anyone ever heard of world wide visa/passport? Does anyone know if this is as hard for a Nigerian to get?