You can set an initial or default value for a field, depending on its data type. This is set when you are formatting the field (see Data types). Later on you can reformat the field to change the initial value. To do this just type the new default in the Initial Value box in the "Format Table" dialog for the relevant field.
Every time a new record is added to a table, all the fields that are formatted to have initial values will automatically be updated. You can of course replace an initial value in Table Grid View by entering an alternative value.
Note: Initial values must be compatible with the data type of the field e.g. characters for a Character field, numbers of the right format for a Numeric field, dates of the right format for a Date field, and so on. When you change the default value of a field, only new records receive this value; existing records retain their old values, which may be there through the old default or because they were directly entered by you.