Welcome to the world of fishkeeping.
You're definitely not ready for fish yet, as mentioned above. You have to cycle the tank first. Please read these articles:
Goldfish require a larger tank than you have. Just one requires 20 gallons.
We can help you pick fish out after you've cycled. Let us know what other species you might like.
75: blood parrots, featherfin cat, emperor tetras, turquoise rainbowfish, BN plecos, japanese trapdoor; 46: WCMM, gold inca snails, ghost, bamboo & amano shrimp, kuhli loaches, rummynose & ember tetras, endlers, platies, flame gourami, guppies; 16: pygmy, peppered, loxozonus corys, otos, assassins, RCS ... ~ Research PRIOR to purchase.... ~