In this article, you will learn to import data manually using an external file. If you expect to import data frequently, you could automate this process to avoid repeating this task. If you want to import contacts, see this article instead.
To import data into a custom table, the current project must have at least one custom table. Otherwise, no import target option will be offered. The fields of your custom table will be used to host the imported data. The fields should have a compatible type (number, date, text) with the corresponding incoming data.
Step 1: Create an Import File
The file to import must be an Excel format (.xls or .xlsx) or a .csv format (comma-separated values). The size of the file must not exceed 50 MB. This file can be compressed to the .zip format if needed (not locked with a password and containing only one file). In the following steps, we will be using the data from the following Excel file as an example: 
Go to Project -> Relational Data and click Import:
Choose the Import from file option:
Choose Simplified mode.
Upload the file:
Choose the option that corresponds to your situation:
If this is your first import, choose the default option (Add and update rows).
Step 3: Map the Fields
Assign the fields from the import file to their destination in the table fields:
If you are importing dates, choose the format from the list or indicate the format used with the Other option.
Step 4: Confirm the Mapping
Once the mapping is processed, you must approve the import.
You don't have errors?
Make sure the fields have been mapped to the correct destination by checking the preview:
You have errors?
You have 2 options to arrange this: go back to the mapping (click Modify) or upload the file again (if you click Details, you will see the Upload the corrected file option):
You could also choose to ignore the errors and launch the import. The data in error won't be imported.
Results
When the import is completed, you can see a summary:
By clicking Consult, you will get a detailed list of the added or updated data. Note that after a few days, this information will be erased to release space on the server.
To consult the list of imports, go to Projects -> Imports/Exports, then select Imports:
Next Step
To avoid repeating this process, you could automate your imports. It is also possible to import in real-time by making calls to the web services using an API key.
Now that your custom table contains data, you could use these data to target contacts.