I've never grown calendula indoors, but I've found them to be relatively undemanding when grown outside in soil of reasonable fertility.
Make sure the pot is big enough and has sufficient drainage.
If you didn't plant it into potting soil that has any kind of added fertilizer, or you didn't use any compost, then you may want a small amount of some low-analysis balanced organic fertilizer once a month or so.
Be careful not to overwater.
If it's growing well, and continues to grow well, you're probably already giving it what it needs. If the plant's health starts to decline, then make sure you aren't overwatering, and consider adding a small amount of fertilizer. (It won't take much for a single plant in a small pot -- follow package directions.)