If I understand your question correctly (you didn't give a lot to work with) you're looking for something like this:
SqlDataAdapter da = new SqlDataAdapter ("SELECT * FROM Table WHERE column='@varNameHere'",con);
Essentially, you'd need to modify the correct command type within the adapter with the parameter you wanted to add... I am not 100% sure because I haven't tried to manually override the default adapter methods recently but you may also need to actually set your SELECT statement with the use of the following instead of in the actual adapter declaration in order for the SelectCommand methods to work as well:
da.SelectCommand.CommandText = "SELECT * FROM Table WHERE column='@varNameHere'"
Hope this helps (and hope I'm not butchering it at the same time) :)
EDIT: As I thought (and as saravind pointed out before I could finish typing my reply) you do need to set the CommandText separately instead of in the declaration of the adapter when using parameters :)