Manna is a kind of a sweet gum and salwa is quails...
Surah 2 verse 57 talks about it
..And we sent down 'manna' and 'quail' upon you,..."
"...(saying): Eat of the good things We have provided for you.'..."
In order that you may enjoy of the pure delicious nutritious sustenance andmnot disobey Him. Yet, they were not thankful to Him.
"...(But they rebelled); to Us they did no harm, but they were putting themselves to destruction."
The terms 'manna' and 'salwa' are differently interpreted by different philologists and commentators. However, the fact is: 'manna', and 'salwa' refer to the heavenly provisions the Israelites were provided with, without any strain or burden on their part.