Imasu/arimasu (iru/aru) are used to tell that something exists. It's usually used in the sense of "there is" or "I have." Imasu/iru are used for living things, people, animals. It's also used for ghosts and stuff like that too, so those kinds of things are "alive" too. [Asoko ni inu ga imasu]: There's a dog over there. [Tomodachi ga sannin imasu]: I've got three friends. Arimasu/aru are used for everything else. Holiday gave some examples for aru. Desu/da is the copula. It means "is". You could say "Amber desu" and it would mean "I am Amber".

imas for... I'm home now - ima uchini imasu. Where are you now? I'm at a shopping mall. - shopping mall ni imasu. arimasu for...There is a pen on the table - Table no ue ni pen ga arimasu. Do you have something to write? Yes! I have a pen. - Pen aruyo (arimasu) desu for... This is the photo. - korega sono(=the) shyashin desu. Sorry by my poor English! It's more difficult to teach than i thought!! I hope anyone could help you better than me...by good english..