I am interested in gaining more definition in my stomach and chest area. I suppose I would like to work towards having a well defined sixpack, although that is not as important to me as gaining some more definition in general.

I'm generally considered skinny at just over 6 feet (183cm) in height and 175 lbs(~70kg) give or take. I'm not overweight at all, yet I also don't seem to have any definition.

What exercises can I start doing each day to improve this and for how long?

In what amount of time would I start to see results?