sawhorse!

Fischer projection is how you would look at the compound from above. Sawhorse projection is how you would look at it from a side. And you can rotate the compound in sawhorse by 60, 120, etc. degrees.

arey so from first sight only say in 1st one OH should be on left na....

pritish plz tell???

Theek toh hai? I didn't get what you wanted to ask..

arey we know that horizontal grps come out of paper na.....so y they put -OH on right!!![we dont rotate it na.. [2]

lol that is when you assign the priority...priority is not assigned here or H would be on vertical line.
Imagine looking at the Fischer projection slightly from an angle. This is how it would look like. Problem is sawhorse is more flexible representation than Fischer (as in we can rotate the groups)