Questions about starting a new medication or concerns about your attention span or ability to concentrate are general questions that are best answered by your primary care doctor
To answer your specific concern, the medication Adderall does contain two different forms of amphetamines. Amphetamines can be addictive and should not be used to treat medical conditions without a physician's supervision, but Adderall itself can be very effective in the treatment of attention deficit and hyperactivity disorder (also known as ADHD).
If you feel that you are not able to concentrate or focus on activities in a way that is disrupting your ability to work or handle higher education, you should consult your primary care physician
for a more detailed evaluation. Your doctor can take a more detailed history and physical exam to try to assess whether this is a new change in your overall health or whether this might be an issue that goes back to childhood. Adults can have ADHD, and recognizing and treating this condition appropriately is important.
There are also strategies for improving concentration that can be used by anyone, whether or not they also have other conditions that may affect their ability to focus. Getting enough and quality sleep; maintaining a healthy, balanced died; and avoiding distractions when working can all be very helpful. Medications to improve concentration should only be prescribed by a physician after determining that there is a medical reason to treat a condition that may result in decreased concentration.