Here's some more detailed instructions for KML upload if you are having difficulties uploading. Note: PastureMap will troubleshoot for you if you are a paid subscriber.
Using Google Earth
Select only the pasture files. You may have other things pulled up like waterlines. Make sure they aren't selected.
Make sure they are drawn as shapes, not lines or pathways. If that's not the case, you can use this website to convert them so long as all of the pathways are connected (ie there aren't any gaps in the polygon shape). But before you do...
Export as a KML, not KMZ. This applies for uploading to the app or to any online conversion tools. You can also use this tool to convert a file to KML if you are given a shapefile or KMZ.
Upload to PastureMap. From your web account, select 'Upload KML" from either the Map or Pasture portal. From the Pasture portal you can see all of your pastures with the perimeter and area calculated. In the example photo, the user also has added in objects. You can add these in the map view if you are a paid subscriber.
As mentioned above, you can use free online tools to convert shapefiles (.shp) into KMLs for upload. If you have difficulties, make sure that all of the files are saved into one folder and zipped before sending.