not able to make head or tail (out) of (something)
Failing or unable to understand, decipher, or make sense (of something) in the slightest. We tried identifying the heiroglyphs on the ancient tablet, but they were so archaic that we weren't able to make head or tail of it. See if you can figure out what this contract is saying—I wasn't able to make head or tail out of all that legal mumbo jumbo.
not able to make head or tail of something
Fig. not able to understand something at all. I couldn't make head or tail of the professor's geology lecture this morning. Can you help me fill out my tax forms? I can't make head or tail of the instructions.