The anticlines represents ridges or folds of stratified rocks, with the strata being sloping downwards from the crest.
The synclines represent through or folds of stratified rocks, with the strata being sloping upwards from the axis.
Both of these features are formed in the same manner, by compression. They are also part of a same geological occurrence. Both of them are curved, and seen from side perspective, they are representing one whole, and they look like a wave.
The difference is mainly that the anticlines are always above and they slope downwards, while the synclines are always on the bottom and slope upwards.