There are so many options for cutting out your printable designs. You can use a paper trimmer for straight lines and scissors for more intricate objects. If you plan on creating party printables, get a 2” round hole punch for cupcake toppers and gift tags. It's a minimal investment that will save you hours of time, and your hands will thank you. Also, check out the hole punch aisle at your local craft store for more options.
You can learn to design printables with free options like Canva, or Paint. These programs are fine for basic designs, but can be very limiting. If you would like completely custom designs, programs like Adobe Photoshop and Illustrator are excellent.