Resources: help, adding packages
Help documentation
Stata's built-in help documentation is fairly extensive; being able to read the documentation will help you in your own troubleshooting. To access the help documentation, go to the command line in Stata and type help and the command you need help with.
help ttest
In the documentation, you will see optional inputs in [square brackets].
For example, you could use a two-sample ttest to look at the effect of sex on blood pressure
sysuse bplong
ttest bp, by(sex)
...and you could use an if statement to restrict that to a given age group. (Note that "if" is in square brackets in the documentation.)
ttest bp if agegrp == 1, by(sex)
Finding and installing packages
There is an active Stata developer community, building packages to help with data management, analysis, and visualization. These additional pieces of code (packages) are available free of charge and can be downloaded through Stata to your computer.
(Note: If you are using one of Reed's computers, e.g. in the IRCs, you can download packages to the machine, although they will be wiped from memory when you log out. If you find yourself using a particular package often, contact Kristin and she will work with CUS to add that package to all the IRC machines.)
One package that is popular for making tables of regression results is outreg2. This is not included in Stata, so you have to go find that package. Stata will look for any occurrence of "outreg2" -- including help files, packages, and articles in the Stata Journal and Stata Technical Bulletin.
findit outreg2
To install outreg2, scroll to "outreg2" under Web resources from Stata and other users and click on that link. This will take you a new page; scroll to the bottom and click on "click here to install".
Additional resources
List of possibly-useful packages (UCLA)
More in package installation (UCLA)