K-1 Disposition of Partnership Interest

I've been struggling to understand the IRS instructions but am totally confused.

Several years ago I purchased a partnership in an oil well joint venture.  It never made any money, went bust last year. I have a Final K-1.

 

My problem is understanding the Basis of partnership interest. Is that simply what I paid for it?  Is the difference between that and the $0 I was paid, ordinary loss, or long-term loss?

 

I'm grateful for any attempt to explain this to me.