Using a Variable in a Query

Hello all,

I have been attempting to insert a variable into a query and have found many different posts around the internet telling me to do it many different ways. For example... if I had the query

select veg_cat_code from geo_feat where geo_feat_id = '5';

I want to have it be

select veg_cat_code from geo_feat where geo_feat_id = 'variableToBeQueriedWith';

I can't seem to find out how to do this. I've read that

select veg_cat_code from geo_feat where geo_feat_id = '${variableToBeQueriedWith}';

would work but it gives me an error. Any and all help is much appreciated!!