Punjabi is a tonal language, which is unusual among Indo-Aryan languages and is the feature that most surprises people learning it.
It has three tones: level, high-falling and low-rising. They arose historically from the loss of the voiced aspirate consonants, gh, jh, dh, bh, whose aspiration was transferred to the vowel as a pitch change.
Neither Gurmukhi nor Shahmukhi marks tone. The letters that once carried the aspirates are still written and are now read as tone carriers, which means the script encodes the history rather than the pronunciation.
The result is that ਕੋੜਾ can mean whip, bitter or leper depending on tone, written with different letters that a learner will read identically.
Native speakers are usually unaware they are producing tones at all and will deny it if asked.
This is one of the reasons Punjabi is harder to learn from books than it looks and one of the reasons it is not well described in most teaching material.
Punjabi is tonal, which most speakers do not know and every speaker uses. The old voiced aspirates became tones, so the same consonants and vowels carry different words at different pitches.
The standard examples pair a level tone with a falling or a rising one. The written form is the same and the meaning is not.
Gurmukhi records the tones indirectly, through the letters that used to be the aspirates. Shahmukhi does not record them at all, which is one reason reading across the two scripts is harder than transliteration makes it look.