quite simple, use something like the following, if you post your table name and field name you want to query then i could write it for you.
SELECT field1.table1
FROM table1
WHERE (((field1.table1) Like "*" & [forms]![form1]![txtfield1] & "*"));
This will look for a value in the form and search for that value within the field
if you want an exact match then use
SELECT field1.table1
FROM table1
WHERE (((field1.table1)=[forms]![form1]![txtfield1]));
The [forms]![form1]![txtfield1] means. Leave the [forms] alone do not change this.
[forms1], is the name of your form which you are referencing to
[txtfield1], is the name of the control on your form that you are referencing to
I hope all this helps.
any issue let me know