20 year old beginner. I want to start buy purchasing a small apartment how should I go about this. ADVICE

a 1-4 unit complex is residential, not commercial so conventional financing is where you would get funded. What state?

If it is only 4 units, a community bank in the area of the property should be able finance it. As part of your due dilligence/research, you should be requesting income statements and a rent roll on the property. Make sure you will have a good debt service coverage (NOI/yearly debt service costs). Then approach the community bank for assistance. They will want to look at your personal cash flow after that.
One other thought, make sure the rent roll shows long term tenants in place. You will also want to make sure the Tenants are financially strong, aren't late on payments, and aren't about to leave. Hopefully the leases were written with the owner able to request the Tenant's financial statements otherwise it will be difficult to tell if the tenant is making money or not (for privately owned companies anyway).

P.S. The Tenant financial section of my answer was for if the property is commercial in nature. For a residential quad-plex, ask for an aging report showing if the tenants are late. The seller will probably then verbally tell you, but I'd prefer something in writing.

I only sell multifamily real estate. Get educated read some books check out some blogs like www.MikeBolen.com and then find a competent real estate specialist who works multifamily to guide you. I have a referral network all over the country just let me know where and I can help you get connected.