This revision aid for L1/L2 (mainly L2) Pearson Edexcel Functional Skills maths gives a side-by-side comparison of perimeter, area and volume, the sort of units that would be involved with each and a worked Functional Skills example of each with a PAV mnemonic for remembering which is which. I have also looked through the last few years of Pearson Edexcel FS for the sorts of questions that require each one.
Note: All images from Pixabay, so do not need crediting.
FM Complex multi-step problem(s)
FM L2.3 Evaluate expressions & make substitutions in given formulae in words & symbols
FM L2.16 Calculate perimeters & areas of 2-D shapes inc. triangles & circles and composite shapes including non-rectangular shapes (formulae given except for triangles & circles)
FM L2.17 Use formulae to find volumes & surface areas of 3-D shapes inc. cylinders (formulae given for 3-D shapes except cylinders)