Firstly it depends on what you classify as a small ding

... My experience stops at poly and depending on the core material of your board you may need to use epoxy

; if you don’t know go with epoxy as polyester resin may just eat your foam. For large dings you may need to clean up the damage and fit a new piece of foam… pictures help the detail of a response.
Yes

, you can combine foam dust and/or off cuts with resin to create a lighter mix (hence the word
"mix", not after or before) after which you will need to seal with a top coat of pure resin and preferably a layer or two of glass fibre. BUT there are products aimed at doing this called a multitude of trade names but more or less the same thing such as
micro-balls, microsheres, Q-cells, etc. talk to a local shaper/shop and see what he/she can arrange for you; noting that these products will also cause the resin to set white in colour and its advisable to seal with a top coat upon finishing.
For a first (minor) repair you can't go past a basic repair kit such as an O&E kit, etc. They usually have a list of the proucts inside and a basic instruction manual (inc. Q-cells or the like). Good luck, its not that hard and a great chance for a learning experience

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