I'm a relatively new player. Could somebody please explain to me how the totem beast feat works in Pathfinder and if I can select it as a core Druid? I would like to gain the +2 Str bonus (bear) for my animal companion and for myself. I have heard some players mention I need a belt of strength for this, but I'm not sure what they mean.
The feat in question can be taken by a core Druid as long as they don't have an archtype that removes their animal companion ability.
How the ability works is you can select one of the animal aspects from the hunter class' Animal Focus ability to effect your own animal companion. Upon selecting the feat you can pick from any of the shown aspects, for example you could select
Bat: The creature gains darkvision to a range of 60 feet. At 8th level, the range increases by 30 feet. At 15th level, the creature also gains blindsense to a range of 10 feet.
The feat only grants the bonuses to the animal companion, the druid does not benefit from the bonuses granted.
Select one animal aspect from the list presented in the hunter class’s animal focus class feature. Your animal companion has natural coloration suggestive of this aspect—a bear might have a dark spot in the shape of a bat, or a hawk might have unusual tiger striping in its feathers. Your animal companion gains the benefits of the selected animal aspect, treating its Hit Dice as its effective hunter level for this ability. This bonus doesn’t stack if the animal companion is already under the benefit of the same animal aspect because of the actual class feature.
As for the belt your friends mentioned, that is a magical item that can give +2,4, or 6 bonus Strength. There is also a more advanced version that adds the bonuses to two of the physical stats, and the most advanced version that adds the bonuses to all three physical stats.