Download zip file from your merchant account.
Log into your Google Adwords account
You can either use the file to create a new campaign, or add it to an an existing campaign you have setup.
If you are importing into an existing campaign:
Open your keyword file and change the value in the "Campaign" column in the feed file to match the campaign name you are adding the keywords to.
Remove the second row (the first row of data under the header row) in the first keyword file (this ensures you to not override any existing campaign settings).
Take the file and go to "Bulk operations -> Bulk Uploads" and upload the file and click either Upload and Apply or Upload and Preview.
Note: when previewing the file you will notice errors for keywords, this is because the ad groups that are going to be created in the file do not exist yet and the keyword row will throw an error.
When applied the ad groups and keywords for each ad group should have been created.
You will need to adjust your bids on each ad group and or each keyword depending on your bidding preference.
You can adjust columns in the file like Max CPC to change the bid per row or just on the ad group rows.