but
The German word 'aber' is a conjunction that is used to express contrast or opposition, similar to the English word 'but'. It can be used to link two ideas or clauses together, and it often indicates that the second clause will contradict or qualify the first. For example, 'Ich wollte gehen, aber es regnete.' translates to 'I wanted to go, but it was raining.' In this sentence, 'aber' is used to contrast the speaker's desire to go with the fact that it was raining.
I wanted to go, but it rained.
This example is using 'aber' to mean 'but'. In this sentence, the speaker intended to go somewhere, however the occurrence of rain caused them to change their plans.
He is very intelligent, but he is very lazy.
In this instance, 'aber' is also used to mean 'but'. The person being spoken about is smart, yet despite this useful quality, they also have the less desirable trait of being lazy.
You are right, but I do not agree.
Here 'aber' is used to contrast two ideas. The speaker acknowledges the correctness of another's point, but nonetheless, they still do not agree with it.