she means like plastic plants one would find in a freshwater tank, you know, the cheap looking ones that serve no purpose other than looking pretty.
generally, the plants used are various
Macroalgaes, caulerpa, etc.... Some people even use mangrove trees, which will eventually grow out of the tank.
Most saltwater aquarists prefer to keep corals in way of
macroalgae, keep the
macroalgae in their
refugiums or
sumps, for their filtering purposes. the reason for this being that as they filter out waste, they grow. And since waste s contantly produced, the
macroalgaes constantly grow, sometimes even out of control, and to keep this from happening, they need to be groomed and/or harvested for feeding. Corals do not grow as fast and offer much more color.
Just my two cents, and i dont mean to be rude, i dont really know your exact intentions, but i would go for a freshwater tank if you want plants. For two reasons. 1- Plants come in a greater variety of size and color (at least where i am). And 2- Freshwater tanks CAN BE, and mostly are(depending on size etc..), Much easier to maintain than saltwater tanks; which require alot more care, research and husbandry.
Again, im not trying to be rude or steer you away from the hobby, im just making sure you know that this hobby is not a Fish+Aquarium+Water=happy type of situation, A good
SW tank needs constant care, research, consideration, and money (!!!! on the money part, trust me

) .
Hope this Helps
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Josh Small Frys 120 Fish- 2 Percula Clowns, Hippo Tang, Black fin Shrimp Goby
Coral- Green and Pink Frogspawn, Colt Coral, Zoanthids, Fungia coral x2
Clams- 1-4.5" Crocea Clam, 1-6" Maxima Teardrop
Cleaning Crew- 20 snails, 6 monster blue legged hermits
more to come i hope