I'm absolutely new to fitness and want to start exercising. So which should I start first? I want to build lean masculine body.
Both cardio and strength training can be an excellent way to improve your physique, it all depends on what you like to do. Lean muscular body mass can be done by doing cardio for say 30 minutes a day and focus on 45 minutes of moderate to intense strength training.
At first start out with light weight until you get a feel of the weight, you can then gradually increase weight.
If you are not a big fan of cardio, you can try decreasing rest intervals with strength training keeping the rest between sets to around a minute, this works well letting you burn fat and increase muscle.
One training method I have implemented recently myself that has helped me not only drastically increase strength, it has also helped me increase lean muscle mass. It has been practiced by famous bodybuilders like Mike Mentzer and Dorian Yates, its called HIT training, also known as "high intensity training". The important thing is regardless of what training method you decide to adopt is to be consistent and you will achieve your gains, it just takes time.
As for a beginner, I'd suggest you do both: Cardio and strength all-in-one!
This can be achieved on the spinning bike (by increasing its resistance), on the step machine or on the rowing machine.
Also, hill climbing (essentially running upwards) is considered cardio and strength as well, just read my post about hill climbing here.