First you will need to make sure you have installed our free CSV Inventory Upload add-on. This can be done under Settings > Add-Ons, https://app.ammoreadycloud.com/settings/addons
Once you have the add-on installed, you can generate a new import by going to the Inventory tab, and clicking the New Import button.
Then select the file you want to upload and your mode of import, and click Upload. For info on import modes, click here
It can take a few minutes for the import to finish, depending on how large the file is. You are able to view the status of your import by clicking the Batch Imports button in the top left corner, https://app.ammoreadycloud.com/manage/batch_imports
Once your import has finished you can view your products under the Inventory tab.