You can demonstrate that you're engaged and focused by:
1) Starting a particular task and working through that task consistently until it's done
2) Giving your full attention to a particular task for meeting; this is, if you're doing a task, you're not multi-tasking and trying to do more than 1 thing. If you're in a meeting, you can show you're engaged by maintaining eye contact with the speaker.
3) Best way to demonstrate you're engaged and focused in anything is to ask good questions about whatever you're doing!