API Access Token
You can get this key from your account at ("API Access Tokens" item from the left side menu). Do not share it with third parties you do not trus - as this key is private and issued only to you.

Also known as cron job. It is a time-based job scheduler in Unix-like computer operating systems. Users that set up and maintain software environments use cron to schedule jobs (commands or shell scripts) to run periodically at fixed times, dates, or intervals.

Heartbeat CRON
Heartbeat is a script and acts like a scheduler - schedules and executes tasks. It does not import / export all products every time it is executed. Heartbeat command needs to be executed periodically by your server. If heartbeat is not working - no tasks are being executed.

Heartbeat Time-out
Determines the maximum duration of Heartbeat execution.

A sub-set of products to be exported / imported. For example if you are going to import 5000 products, than Heartbeat will process this task in batches of 500 (in total 10 Heartbeats to process all 5000 products).

This is where you would set up how and when you want to import / export your products. Import / export tasks are executed based on your preferences in profiles. You can have multiple profiles for import and export.

Tasks are scheduled and executed by Heartbeat CRON. You can set how often import/export task needs to be executed in your Profile preferences.