1. To be enthusiastic and interested in what you are doing or will do, or to want to do something very much. English = (be) keen, (be) eager.
2. To have interest in something. English = (be) interested in.
3. To be happy to or be interested in doing something. English = (be) glad to, (be) keen to.
4. To have no objection to doing something you have been asked to do. Idiomatic English = (be) glad to do something, (be) happy to do something.