Sometimes, the word "along" is used when talking about something that has a certain length, or covers a certain distance: "I walked along the street."
Sometimes the word "along" is used with "come": "There is a party at my house. Why don't you come along?" This has basically the same meaning as: "Why don't you come?". The word "along" doesn't really add any further meaning!
Sometimes the word "along" is used with "with". (Or I could say ... "Sometimes the word "along" is USED ALONG WITH "with"!). For example: "You must bring your application form, along with some identification." Once again, the word "along" does not really add any meaning. It just makes the grammatical function of the word "with" slightly more clear. Here's an example:
"Bring me bread, with speed!"
This could mean "Bring me bread quickly" (the phrase "with speed" modifies the verb "bring"). However, the word "speed" can be used as the name of a drug, so it could mean "Bring me bread, and also bring me some of the drug called speed". Now compare this: "Bring me bread, along with speed". In this case, the word "along" makes it clear that I want you to bring me two things: bread and speed. It can't be interpreted as "Bring me bread quickly".
I hope this makes sense!