When applying for a US visitor's visa check to see what the exact requirements are for your nationality. Some countries are on the US Visa Waiver program which makes the process much easier for visitors.

But if you do need a visa, you will need to satisfy the embassy/consulate visa interview officer that you meet all the criteria for a US visitor's visa which includes a valid identity, no criminal background and have a valid reason for the visa. As an 18 year old you can apply on your own. The key success factors for the visa to be granted is to show evidence that you have sufficient funds to support your trip to the USA as well as evidence of strong ties back to your home country (for example you have family and proof of employment back home) which shows the officer you intend to return home after your vacation. If you have a proposed itinerary or a letter of invitation from US friends, it helps to bring that to the visa interview.

I've never heard of the I-134 being used in conjunction with a visitor visa application but it has been years since I've had to deal with CBP/INS. Typically it is used by a US citizen/permanent resident to demonstrate willingness to provide financial support for permanent resident applicants.