How does it make me feel more energetic?
Your body has a system to tell how much energy has been used by activating certain receptors on your nerves that bind to the adenosine that comes from the high energy molecule ATP or adenosine triphosphate when broken down. When enough of the receptors activate they put a break on the pumping of energy in your body making you tired and sleepy making you take rest.
Caffeine has a similar structure to adenosine making it being able to go in the receptors without activating them therefore blocking them until your body can breakdown the caffeine usually taking 4-5 hours keeping the energy pumping throughout the body without any restriction till then.

Are there any side effects?
Well yes of course there are side effects for that constant pumping of energy mostly giving you high blood pressure, and inadequate rest leading to giving or worsening your anxiety, headaches and nausea but all of these are temporary what isn't temporary though is the effect this can have on growth for children and teens because you need rest and adequate sleep for growth and caffeine takes that rest and sleep away from you.
How much is too much?
The average toxic dose of caffeine is 10g which is around 10000 cups of coffee but 5 cups should be enough for giving you all the severe side effects like anxiety and blood pressure mentioned above.

Caffeine addiction:
Drinking caffeine to block the receptors regularly makes the body make more of these receptors to compensate for the blocked ones and that requires even more caffeine to block so you might have started with one cup of coffee/tea in the beginning but that doesn't have the same effect on you anymore leading you to drink more and more and one day without and caffeine would make you extremely tired and sleepy.

Can I overcome this addiction?
Yes, and its much easier than overcoming addictions of any of the other extreme stimulants like nicotine found in cigarettes and cocaine. You just have to give your body one week of minimal to no caffeine for the amount of receptors to go back to normal and that's it.

Caffeine in sports:
Caffeine can have an impact on your performance especially if you are a regular caffeine consumer as drinking caffeine can make you less tired and therefore faster in certain sports while it won't improve your strength.
How fast?
On an experiment I did with running 650 meters with and without caffeine for a regular consumer; it improved speed by 20 seconds!
If you are more interested in the effects and working of caffeine you can check out this presentation made by me :)