[noun] + が + ございます [noun] + で + ございます [noun] + は + ございません
ございます is a more formal あります: something is there, or someone has it. You hear it from shop staff, hotel desks, announcements and business calls, said about the speaker's side – the shop's stock, the building, the company.
The negative is ございません, in place of ありません.
After a noun, でございます replaces です at the same level of formality.
でございます is polite by being modest about your own side, so it cannot describe the listener. Asking a customer who they are takes the honorific でいらっしゃいます.
An い-adjective before ございます changes its ending, and three everyday greetings are fossils of that: ありがとうございます from ありがたい, おはようございます from はやい早い, おめでとうございます from めでたい. Outside these phrases the adjective form (おいしゅうございます) sounds old-fashioned.
Outside the greetings, ございます does not belong in conversation with friends or family; there it sounds stiff or sarcastic. Plain ある and だ or polite あります and です are the everyday forms.