I am getting use to Lightroom but I am stuck, how do you re size ?
I assume you don't mean Crop.
So to resize a photo :-
Make sure you are viewing it in the Develop Module.
Then select File - Export
This will open a new window.
Here you can give the file a new name or change its type to JPG or png or whatever.
If you scroll down the window you will see a sub section called Image size.
In this section you can choose what size you want.
Then when you have everything set up you click the Export button at the bottom.
There are some standard presets that you can use by selecting File - Export with Preset.
Or you can even create your own Preset if you want to use specific settings over and over again.
hope this helps.