Well in short what you probably need is a DAW or music notation program. There's a lot of options but most types of programs that fall into those two categories will do what you need at a minimum.
If you're on a mac the cheapest thing you can use is Garage band which costs.......£0. It should notate a piano part and you can certainly add effects such as reverb.
On a pc there's no free DAW that springs to mind but you could try cubase out for free for a month by downloading the demo.
These are just a couple of options, ultimately if you wanted to go deeper probably something like logic is the best choice on a mac and cubase on a pc as these are what most professionals use for composing with score notating facilities.
But start cheap with a budget program and see how you get on, there's certainly no need to run out and spend hundreds of pounds on software until you get a feel for what you actually want from that software.
Tom McFall is an engineer, producer, and songwriter who is working with globally successful artists like REM, Snow Patrol, Bloc Party and Biffy Clyro. He is also a music production tutor at British & Irish Modern Music Institute. Discover Tom’s work on his website: https://www.tommcfall.com/