First, note my comment to your question. I have the EF 75-300 lens which I bought 5 yrs ago with my old Rebel XT. It served me very well at the time. For a first tele lens, this is not a a bad choice at all, especially given its low price.
You will find in time that its quality is mediocre compared to more expensive teles. But, take your time enjoying your new equipment. If you buy this lens, remember that even if you come to a conclusion that it is not what you need, the "damage" is not that great, and you can always resell it and get back some of your investment.
Coupled with the 18-55 "kit" lens, you'll have enough gear for a couple of years.
Aside from that - the lens' zoom number relates to the ratio of the long focal length to the short one a zoom lens can be set. So, 75-300 gives you a zoom of x4 and 18-55 gives x3. Zoom numbers are not (directly) related to the lens being telephoto or wide-angle.