Places are the basic structure of Roblox. They are the whole 3D part, but not all are the same. There are "obbys" or Obstical Courses, "Tycoons", where you make a certain object to get money and then use that money to upgrade your equipment to make more money, and so on.
So why should I have a place? Edit
One word, MONEY. Everytime someone visits your place per day you get one Ticket. Robloxian Tickets are similar to tickets you win in an arcade. That way you can buy hats and other things that require money. You also get a 10 ticket bonus just from logging in every day (once per day).
How to edit your place Edit
There are several ways to edit your place. The easiest way is just go to Roblox and use the brownish edit button. That is good if you are making a place that doesn't need many complex scripts. The other way (that I know of) to edit your place is by using Roblox Studio (Start ►All Programs ►Roblox ►Roblox Studio). Roblox Studio is used for major and minor editing of many things as well as the ability to save your place to your computer's hard drive. After you have finished editing your place in Roblox Studio make sure to upload it to Roblox so that everyone else can play it. To do that click File ►Publish to ROBLOX. After selecting that click update in the popup window and select the place that you want to update. Now anyone can play your place