Depending on the type of drum machine, you will need to set that drum machines MIDI clock to external clock and follow the steps for creating a New Instrument with sync options checked:
Please read this article for setting up External Midi Devices with Studio One 3: http://support.presonus.com/hc/en-us/articles/115001352966-Studio-One-3-How-do-I-setup-a-hardware-keyboard-synthesizer-in-Studio-One-3-
Then, check out this article on setting up to record using an External Device: Setting up to record with an External Midi Device Studio One: http://support.presonus.com/hc/en-us/articles/115001418283-Setting-up-a-Song-to-Record-With-External-MIDI-Devices