Simple and straightforward:
* The detective tried to decode the cryptic message left by the thief.
* Scientists are working to decode the human genome.
* I struggled to decode the instructions for assembling the furniture.
More complex and nuanced:
* Her smile was a subtle signal that I needed to decode to understand her true feelings.
* The ancient text was so damaged that it took years to decode its secrets.
* The therapist helped her decode the messages her body was sending through her anxiety.
Figurative:
* The artist's paintings were full of symbolism that needed to be decoded by the viewer.
* His words were a coded message that I needed to decode to understand his true intentions.
Formal:
* The analyst will decode the data to identify patterns and trends.
* The software is designed to automatically decode encrypted messages.
The specific way you use "decode" depends on the context and the nuance you want to convey.