If you've given your child a task only to find out later that they've built a fort, read a book, or used their tablet instead of doing the job, welcome to parenting a child with ADHD.
Kids with ADHD get distracted easily. It's just a fact. They get distracted not because they aren't bright or motivated, rather because staying on a task is not something that comes easily or naturally to them, so it's essential to give them specific techniques that help them.
These techniques can include charts, visual aids, point systems, timers, and an environment that reduces distractions.
For example, if you want your child to clean their room, but they have a TV, computer, tablet, or phone, those distractions will make it harder for them to do what is needed. Instead, by removing these items or blocking access to them and having a step-by-step guide to cleaning their room, you make it easier for your child to do what they are supposed to.
The techniques will help reduce the distractions and make it more likely for them to do the job, but they still need consequences if they don't. 
The skill of Effective Negative Consequences helps you determine consequences that matter to your child. If screen time or time with friends is important to your child, losing them motivates them to do better in the future.
The goal of Effective Negative Consequences is to teach your child, not to punish your child. You can find more about the skill on SmarterParenting.com.