Linking Records Using the Record Link Field
Linking records from other apps on the mobile device are similar to selecting a choice value. When you come to the record link field you may have two options, to either select existing records or to create a new record.
Selecting an existing record will open a pick list, that can be searched. Once selected the record will be linked to the record you are creating/editing. If you have the option to link multiple records enabled you will be able to link another record.
Selecting to create a new record will take you to the record editor in the linked app and allow you to enter in the data you wish to capture to that new record. Once you have finished you can save the record and it will automatically be linked to the record with the record link field.