How to differentiate alpha and bita glucosidic linkages....

First and foremost a glycosidic bond is such bond that is found in sugars, for instance such bonds are found in cellulose, cellobiose, chitin and the likes. Mostly could be seen in the cyclic sugars I mean the pyranose and the furanose being an aldose and a ketose sugar respectively, and examples of such bonds are the alpha (1,4), alpha(1,6), and beta(1,4).Note that cellulose, glucose have a beta(1,4) linkage, how the the beta -OH of the first interacts with the -OH of the 4th carbon.For an alpha(1,4) linkage the alpha -OH on first carbon reacts with the -OH on the first carbon of the other cyclic sugar.As for the alpha(1,6), it is present in a branching glycogen, where 3 pyranose are involved, the one above has its alpha hydroxyl on the first carbon reacting with the 4th carbon of another pyranose which is already in an alpha(1,4) linkage with another pyranose. See cell biochemistry for more explanation.