Windows 7 is very different to XP and while it is similar to Vista, there are still plenty of differences too. Sometimes you will be lost and you won't be able to find something that you know is probably there, but you just can't find where it is. Dialogs or features that were in one place in XP or Vista are now called something else and are not in their old position.
In XP the only way to find programs and features was to look on the Start menu and browse all the programs, then open the Control Panel and go through all the items there too.
It was hard to find things sometimes. Windows 7 solves the problem by adding a really powerful and useful search box to the Start menu. Now you don't need to manually search for things, Windows does it for you.
The Search facility is far superior in Windows 7 and you can find a lot of things by clicking the Start button and entering a word or phrase that will identify the item you want.
The Search function isn't a dumb word matching search and it has some intelligence.
For example, if you enter
customise you'll find that a list of results are displayed that include Add gadgets to the desktop, change the theme, change the power saving settings, change the screen saver, and so on.
All these are customisation features, but the word 'customise' doesn't actually appear in any of the results.
In Windows XP you will be used to clicking the Start button and then selecting the Run menu option to enter a command like
cmd (open a command prompt window),
msconfig (run the startup configuration editor), or
regedit (run the registry editor).
Like Vista, in Windows 7 the Run command is on the Start, All Programs, Accessories menu rather than on the Start menu. However, you will find that you don't need it as much because the Search box can act just like the run box.
For example, if you enter any of the commands above into the Search box they will do exactly the same as if you had entered them into the Run box.
So most of the time you can just click the Start button and type in the command that you want to run. It is a sort of combined search and run box. It searches as you type, but when you press Enter it executes what you have typed as if it was a run command.