Help with exercise

Hello,
I'm looking to step it up a notch!
I'm not overweight by any means, but I would really like to tone up my body and build some muscle. I'm slim but it's flab! I love cardio exercises, but am absolutely clueless about any kind of strength training and I am kind of thinking that's probably what I need to be doing. I currently don't have a gym membership as I'm not really sure where I will be living- hopefully that will be solved in a few weeks. At the moment, I am living with a friend in a tiny apartment, so I am looking for something I can do in a small space.
Any suggestions?
Thanks

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