I would say, in Japanese, the postposition/particle「と」"to" has a meaning similar to "and" in English, while the phrase「~と 一緒に」"~to issho-ni" has the meaning of "together with..." as mentioned by the above respondent. There is also another postposition/particle named「や」"ya", and it means also "and" in English. However, if I recall it correctly, when「と」is used for expressing a number of things, it is required to list out all of them; while for「や」, there is no such restriction. For instance,
1) 貴方は 明日 私と一緒に 図書館に 行きませんか。= Would you like to go with me together to library tomorrow?
2) 私は りんごと 苺と オレンジが 好きです。= I like apple, strawberry and orange. (i.e., only the mentioned three things are my favorite fruit.)
3) 私は スーパーから 沢山の物を買った：野菜や 牛肉や 果物や 等だった。= I bought a lot of things from the supermarket: vegetable, beef, fruit, etc. (i.e., I bought a lot of things, but I could only list out the mentioned ones.)
I am not very sure about the structural correctness in e.g. 3), but at least you may have an idea the sort of differences between「と」and「や」.
N.B. 「と」also has a function of "that" to link a subordinate clause into the main clause. For instance,
(私は) 君が/貴方が とても 美しいんだと 思います。= I think that you are very beautiful. (This could be a good sentence if you are about to chase some look-gooding Japanese chicks, or any ladies that understand Japanese in general :)