The first thing you should do is put together your Excel or Google Sheets spreadsheet with the content you'd like to post. You can learn how to put your spreadsheet together here. Once you load your file to Postcron, each row of the spreadsheet will become a different post, so if you have 5 rows, you'll have 5 posts.
Once your spreadsheet is ready, log into Postcron and go to the Bulk Uploader section. Make sure you select the social accounts you're looking into posting to by clicking on them on the account selector and then click on Upload CSV file, choose the correct file, and confirm.
If you're scheduling Instagram posts or Facebook Page posts, make sure you select whether you want to schedule your posts to your Feed or Stories. If you have a Business-type Instagram account selected, you can choose whether you want Direct publication or through Notification.
Postcron will process the file and you'll have a chance to check your posts and edit them if needed. Once you're done, click on Save and Schedule to schedule your posts, or if you'd rather just save these posts for scheduling later, click on Just Save, name your file and click on Save.
Your Bulk file will get saved to your Postcron account, and you'll be able to easily reuse it in the future if you need it.