The mixer's 1/4" inputs can be used with a tablet or laptop, but keep in mind that it is mono.  If you use a 3.5mm TRS to 1/4" TRS cable, the left channel will go through the mixer.  The mixer input jacks' ring terminals are not connected, so it will not short your source's right output.

Examples of cables are the Hosa CMS-103, CMS-105, and CMS-110.

Another option is to use a 3.5mm TRS to dual 1/4" TS insert/Y-cable.  In that case, you can connect the left, right, or both channels to mixer inputs.