As given in your question, when も "mo" is used in affirmative sense, it means "too" or "also". When it is used in negative sense, it has a general meaning of "not ... at all". For instance, 何でも ない。(nan demo nai.) = There is nothing at all. 私は どこにも 行きません。(watashi-wa doko-nimo ikimasen.) = I do not go to anywhere at all. Sometimes, when it is used in questions (interrogations), it has a meaning of "even" or "even if". For instance, 英語で 話しても いいですか。(eigo-de hanashitemo iidesuka?) = Is it alright (even) if we speak in English? [This was what I usually said years ago when I visited Japan with very limited conversational ability using solely Japanese. :)] N.B. I encourage any Japanese speaking members to provide further examples or usages, should I have missed any information. Good day. / 良い一日を。

Just in addition to mitong's answer... If used after some numbers such as quantity, length, duration etc,'mo' means 'as much as'. The number is something more than the speaker expected or than normal. きのうは　２じかんも　べんきょうした！ I studied as long as 2 hours yesterday!