My Own is the currently selected field ownership projection: how often SaberSim expects the field to roster a player. Projections in this column can be modified manually, and users on the Ultimate Plan can choose different ownership sets that model how the field is expected to play in different contest sizes and stakes when available. Also note that any rules you set around ownership will use the ownership in this column.
Adj. Own (short for adjusted ownership) is that same ownership adjusted for how the player actually performs in the simulations, so it tells you whether the field's interest in a player is justified. If a player’s Adj. Own is higher than their ownership projection, it indicates that the ownership “counts” as being higher because they are over-owned relative to expectations, and vice versa.
My Own is not your exposure. Exposure is how often a player appears in your own lineups. My Own is a projection of how often a player projects to appear in everyone else's lineups, and the two get mixed up often.
Both Adj. Own and My Own are mostly there for your own convenience and research, and you can consider them as “summary statistics” that describe things the contest sims are taking into account in a more dynamic and direct way.