Shares

Its basically like stocks. Once people add liquidity to the pool (ATX and SWAP.HIVE) they receive shares. These shares don't change if the price of the token change or any people add/remove more liquidity to/from the pool.

%

Percentage of that account holds of the total liquidity of that pool. This allows someone to understand that when anyone swaps ATX/SWAP.HIVE on the pool and 0.25% fee gets collected from those swaps, that same fee gets distributed by all liquidity participants on the pool in accordance to their respective participation percentage.

Example: If a swap generates 1 ATX of fee, then I will get 0.23 ATX according to that percentage in the picture you posted. Same goes for the other way around swap, if the generated fee is 1 SWAP.HIVE, then I get 0.23 SWAP.HIVE.

Depending on the direction of the swap, people get either fees from ATX or SWAP.HIVE, as the resulting token of the swap.

ATX liquidity and SWAP.HIVE liquidity

How much liquidity each account has on the pool. The values (ratios between how much 1 ATX values in SWAP.HIVE) change depending on the swaps people do. If someone swaps ATX to SWAP.HIVE then that account is adding ATX to all liquidity participants of the pool (divided by participants %), and this causes the price of ATX to go down vs SWAP.HIVE. The other way around if people swap SWAP.HIVE to ATX, as ATX gets removed from the pool, in order to swap it for SWAP.HIVE, the price of ATX (in SWAP.HIVE) increases.

The more liquidity exists, the more stable the prices stay, and the more amount of swap is allowed without big price discrepancies.

Hope it helps :P