I want to import my data from another eCommerce system

A few resources which may help you:

Migrating from another MySQL system
EasyPopulate-Free
EasyPopulate-Advanced
Using Excel to import or manipulate SQL data
Data Manager Tool
SQLYog Windows-based database mgr for MySQL

Using any of those tools will still require that you learn the schema of the Zen Cart database, which is documented in part here
Zen Cart Database Schema

You will need to convert all your data into fields to match appropriate tables/fields in the Zen Cart database infrastructure, and then import the data into your Zen Cart database.