what is best app for partitioning external memory card. for samsung galaxy tab SM-2105

[carmelb]

what is best app for partitioning?
why is it necessary to partition the card for it to be used properly?
the card is 32GB. what size partitions are advisable? and both need to be primary??

This tablet has been rooted.

 

[smitbret]

Mini-Tool Partition Wizard

The Free Version will do everything you want

http://www.partitionwizard.com/free-partition-manager.html

Your other questions are difficult to answer without more explanation. A single 32GB Primary partition (formatted NTFS) is probably just fine for general storage use on your tablet. Fat32 will limit you to 4GB partitions.