How to know which is more stable ?

but in this structure the middle contain CH2OH

In the cyclic form of a sugar, the anomeric carbon is the carbon that was part of the carbonyl group in the straight-chain structure. When the chain converts to a ring, C-1 becomes...

in beta form -OH is at equatorial (red) while in alpha form it is axial. when all the groups are at equatorial then there is no 1,3 diaxial interactions

check it

I can't understand sorry

At equilibrium, the beta anomer of D-glucose predominates, because the -OH group of the anomeric carbon is in the more stable equatorial position of the more stable chair structure...