Best Share is the highest difficulty your miners have solved. If the difficulty exceeds the network difficulty, then you have solved a block and could earn the block reward upon successfully broadcasting your result to the network and after another miner adds a block to yours. Accepted shares is how many shares of work your miners have submitted to your solo pool. If you have multiple miners connected to your solo pool, they will display in the Solo Mining users section and their respective shares submitted and best share result will show in that section.