I have never cooked fish...how do I know it is done

It's flakey

Usually when it's no longer transparent and flakes easily with a fork.

Ya but I generally like chicken..

If your cooking fish fillets it is quite easy. You will notice that your fish flakes like everyone said. Fillets are simpler than fresh fish. Fresh fish requires a longer time line but taste better than fillets. This also flakes once finish.

When it can flake apart with a fork.

Push down in the middle of the fish. If it feels firm its done. Fish doesn't take very long to cook. If you are cooking tuna it is normal to serve it very rare, otherwise it dries out. Salmon can also be serve rare. White fish like tilapia, flounder, basa, can be baked or fried and shouldn't take more than 15 min. to cook.

when it is fork flaky, and not wet or shiny on the inside.

it flakes and is not pink