An example of a software you could use as a midi interface would be xotopad
If you wanna try Ableton live, you could even use something cool like yeco.io (not free)
As you want to send the MIDI information to your macbook, you could use something like midinet, which can be found here: https://www.humatic.de/htools/mnet/man.htm
It is an Windows and OSX MIDI driver that can transfer and receive MIDI information using various network protocols (Multicast, RTP, Bluetooth, ADB, WebSockets and Serial). It can even communicate with other clients on android, linux, windows and OSX
However, I would really recommend using a real hardware MIDI controller as it is significantly easier to set up and use, and much more efficient.
My personal recommandations would be something like a Nektar Impact LX49+, an Akai Professional MPK249 or an Arturia MiniLab MkII 25 if you are on a really tight budget.
These are all USB, and easy to setup in GarageBand.