examples: I would go to Russia if I could. I will go to Russia in one week. I shall go to Russia in one week. I should do my homework, but I would rather watch tv.

will (simple form), would (past): I will do it. I asked him, but he said he wouldn't do it. shall (simple form), should (past): In American English, "shall" is generally found in traditional expressions (e.g., "Shall we dance?") and in legal documents. Modals or auxiliary verbs help to express the speaker's attitude toward action (e.g., ability, permission, obligation, possibility, etc.) The past tense modals are: could, might, would, should. Be careful. The tense of the modal does not always correspond to actual time. Examples: WOULD you LIKE a cup of coffee? SHOULD I LEAVE now?

would is conditional- Its not certain. Will is certain, without doubt that something will happen. Shall is like will, but old english, not really used in modern speech. Should is conditional in the sense , that it would be right to do something, but its not required.