even though it is recommended that first you should understand the concept and then go to solve the problems but for mechanics I would suggest you to directly go to the problems if you are unable to understand the concept because the problems are very well explained and you can visualise what is happening and then you can see the solution if by seeing the solution if you are able to understand the concept then it is good because initially if you can understand the concept by seeing the solution then it is fine I don't think that it is a good habit but don't make it habit of once you are able to understand the concept then you should read whole theory and then go to problems of higher level.