In terms of what it means to be in the 'Limited Capability for Work' group in a practical sense, you will not be required to look for a job, but may be required in 'work preparation' activities which are deemed suitable to you. This could include having to attend workshops/courses etc.
Key issue is that they should not be asking you to do activities which are specifically unsuitable to you because of your disability.
So you need to comply with the requests to avoid sanction, but also challenge any requests that are not suitable.
Hope this helps!