able
The phrase 'in der Lage' is used in German to express the ability to do something. It is often used in the context of 'being able to' do something. For example, 'Ich bin in der Lage, das zu tun.' translates to 'I am able to do that.' Note that 'in der Lage' is a phrase, not a single word, and it requires the use of the verb 'sein' (to be) in the present tense.
I am capable of playing football.
This sentence is used when one is expressing their ability to do a certain activity, in this case, playing football. 'In der Lage' translates to 'capable of' in English.
You have the ability to understand the book.
This sentence is making a reference about someone's capacity to understand a book. 'In der Lage' is used to indicate the possibility of an action from someone's part.
We are able to solve the problem.
In this instance, 'in der Lage' is used to express capability or possible action of solving a problem. It is translated as 'able' in English and it is used when the subject has the capacity to perform an action.