Hi,
you could just make the form bound and then when the record loses focus it
will save the data to the appropriate fields. If this is unbound you could
use code like this:

Dim rs As New ADODB.Recordset
Dim varItem As Variant

rs.Open "tblYourTable", CurrentProject.Connection, adOpenDynamic,
adLockOptimistic

rs.AddNew
rs!Field01 = Me.YourControl01
rs!Field02 = Me.YourControl02
rs.Update

rs.Close
Set rs = Nothing

HTH
Good luck

If you don't want to deal with VBA, you could use a Macro to run a Query.
Create an Append Query based on your table.  Choose your table as the Append
Table or target table.  In the Criteria portion of the Query, you will put
the controlnames as the condition. Exp:

[Forms]![YourFormsName]![YourTxtBox]

Then on the click event, choose Macro.  On the Action pull down, select
OpenQuery.  In the Action Arguments Box at the bottom, select your Query
Name, and Data mode.  Save your Macro and exit.  

When you click the button, it should run the Append Query, and update your
table.  Macros are easy to use for certain situations.  Once you become more
familiar with VBA, it allow you greater flexibility to modify actions on the
fly.  Good Luck!