得 and 不 may occur between the action verb and the resultative endings to indicate that it is possible or not possible to reach the conclusion or result.

To indicate that it is possible: action verb + 得 + resultative ending

To indicate that it is not possible: action verb + 不 + resultative ending

To compare:

我看得懂 I can understand (by watching)

我看不懂 I cannot understand (by watching)

我买得到 I can buy (to get hold of)

我买不到 I cannot buy (cannot get hold of)

e.g.

我看得懂中国电影。 I can understand (by watching) Chinese movies.

英国买得到螃蟹吗？ Can you buy (to get hold of) crabs in England?

吃得出来蟹肉非常新鲜。 You can tell (by eating them) the crabs are very fresh.

他说的话我听不懂。 I can't understand (by listening) what he says.

我找不到我的钱包。 I can't find my wallet.

我想不起来他的名字。 I can't remember his name.

Please note that the alternative 会 to express 'can' and 不会 'cannot' focus on the ability to do something, i.e. whether a person is able to perform something or not, while the above 得/不 structure is about result, whether the result of the action is achieved or not.

Compare:

I can swim… 我会游泳……

…but I cannot swim fast. ……但是我游不快。