help with using STATA

#1
Hi all,

I am graduate student who has just enrolled in a course which teaches STATA. I am having a hard time learning the software.

I have a small part of a dataset (MEPS-Medical Expenditure Panel Survey) and I want to run a few tests on the same. The dataset consists of asthma patients. There is a variable named asstil03-which means "persons who still have asthma". As a first step, out of the full cohort, I want to restrict the analysis to only those who "still have asthma". the coding for the variable is as follows-

-9 NOT ASCERTAINED

-8 DK

-1 INAPPLICABLE

1 YES

2 NO

I am interested in keeping only those who could be listed under 1-YES.
Please let me know how do I do this using STATA. I would be really grateful and would appreciate any help in this matter.

Thank You.