To manually enter gifts via the Gift & Contact Import, first create a new Gift Batch. Then click on the "Create a Transaction" button in the upper-right.
On the gift entry form, enter any combination of Contact data to search for an existing Contact record. After clicking the Search button, if there is a match, click to Select the correct Contact record. The Contact ID field will be populated, meaning that a Contact has been selected and it is time to enter Gift data.
If there is no match, enter as much Contact information as possible into the form and then move on to entering gift data.