You asked

How will ADHD affect my child's future?

ADHD can range in severity. For some adults with ADHD, problems with organisation, concentration, prioritisation and focus may in fact get worse. They may miss deadlines and important events.

On the positive side however, hyperactivity will improve and most adults will be able to sit still though they may still feel restless and feel unable to relax. One of the most severe symptoms for adults is impulsivity, which can cause impatience, mood swings and make relationships difficult.

Adults who have been diagnosed with severe ADHD may find it helpful to follow the following advice regarding employment:
  •  Avoid dull and detail-oriented jobs
  • Structure work environments to reduce distractions
  • Work on boring or repetitive assignments when they are most alert.
  • Make sure assignments are understood fully before starting to work on them
Every parent who has a child with ADHD will worry about what’s going to happen as their child grows up. It’s important to remember that early diagnosis and treatment is instrumental in helping a child with ADHD be happy and successful in their adult life. There are plenty of success stories out there, take for instance the story of American Olympic swimmer Michael Phelps who was won an unbelievable 14 gold medals in the 2004 Athens and 2008 Beijing Olympics. Swimming for Phelps isn’t just a winning sport it’s a way for him to manage his ADHD. Phelps’ mother Debbie has described her son’s exhibition of classic ADHD symptoms including not sitting still and being unable to focus. However, he channelled that into swimming and with continuous support, praise and encouragement he began to cope with his ADHD.

More questions

Getting your child to study and not spend their time on facebook can be difficult but there are lots of things parents can do to promote study. 
It's perfectly normal for parents of children with ADHD to worry about their child's future. 
Depending on what age your child is, there are different signs and symptoms of dyslexia that you can watch out for.