The bulk upload links are found under the (+) button, found on the top right of most pages. Each data type has it's own template and field documentation available within the app. 

Google Sheets is the Google version of Excel. It's cloud hosted and so allows multiple people to edit the same file at the same time. SheepCRM exploits this to import your data and write back comments. In a perfect world your data would import without a single issue. However in the real world data has mistakes and providing feedback on those mistakes was the biggest challenge with uploading CSV file.

The current Google Sheet loader has 'Alpha' status because the user interface is not yet simple enough. It does however unlock some useful functionality not available through other upload routes.

tags, email, telephone, connections and other fields all support multiple values. When uploading a bulk file you need to think carefully about the behaviour you want.

The default behaviour is to over-write or replace the existing fields. Uploading a column 'tags' with a value 'my-new-tag' will remove all existing tags and replace with a single tag.

For multiple values use multiple columns with a numeric postfix e.g. emails.1, emails.2, emails.3 as three separate columns.
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The number after the field name is an index (a counter) into the list of values. If you want to replace values then start counting at '1'. If you want to add values to the list then start with a number that you are confident is above the likely number of values (e.g. 100)
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e.g.
If the data for tags is 

apple, banana, pear 

To delete records in bulk use a column named delete and fill the cells with Y . Be careful, Sheep doesn't offer a bulk undelete.