Anything infected is first hot, red, hurts then pus shows up. Washing and rinsing well then putting on triple antibiotic cream should be done 3 times a day until healed. Wether it should be covered has a rule. If its wet you need to dry it therefore leave open. If its dry keep covered. Use an ointment to keep wet, a cream for drying. If you get streaks going aww way from the area you'd best see a doctor for an antibiotic
Its pretty unusual for a tattoo to get infected because of the sterile process they use. If its infected is this from a home job? Anytime you get an infection from a tattoo you should see a doctor. If the equipment isn't sterile you will possible have other concerns also like hepatitis and or HIV.