I can say that,
"-shita" means always past and its basic form is "desu" and "masu".
*私はパンを食べました。= watashi ha pan wo tabe mashita.= I ate bread.
*私は写真を見ました。= watashi ha shashin wo mi mashita.= I saw the picture.
*あれは犬でした。= are ha inu deshita.= That was a dog.
and "shou"
Its basic form is "desu" or "masu" + "u (auxiliary verb and guess)".
*食べましょう。= tabe mashou.= Let's eat.
*行きましょう。= iki mashou.= Let's go.
*明日は晴れるでしょう。= ashita ha hareru deshou.= It would(will) be sunny tomorrow.
sorry, about "shite", I need some examples.