You haven't provided many details, so I'll guess my best. As far as side-scrolling, simply place objects on a layer and restrict movement to horizontal. Possibly consider the platformer behavior if jumping is appropriate. For the turn-based part, you basically just need a way to keep track of what state the game is in and then instructions for what to do during each state. This can be done with a variable, but you may want to use the Dictionary or Array object to store more data and possibly use it to decide the state of the game. My guess is you may have overall modes, too (ie running and exploring and then it shifts to battles). You'll want to include the events for each mode in a group on your event sheet and enable/disable them when you switch.
Possibly give us some more details so we can fill you in. If this is your first game, you may want to try something simpler or a prototype of a few aspects of your game so you can get some good design practices under your belt and familiarize yourself with C2's editor.