What is the significance of options like "Share" and "More" in document library command bar ?

Welcome Ron to DANIWEB.

I get the feeling that you might have been tossed into the fight without training on these products. What I usually do is click on More to see what is offered. Share tends to always be the same thing where I can give access to the object to another Sharepoint users.

I worry a bit about your question since you claim to be a developer at some place. Are they offering training courses? Take them. If they don't, find Sharepoint training in your town and take a few.