I want to have aquarium with plants in it.
When I'm setting the new tant what should I do with the plants and the gravel? set the gravel with the water and let it work for couple of days or set the gravel and the plants with it and then put the water in? Please help me with this question so I will have no probelm with the plants and gravel set-up.
Plants can be a little complicated… you'll want to spend some time browsing in the Plants forum.
I find it easiest to fill up the tank while planting. Put in the substrate, bring water level up to top of substrate, plant low plants, bring substrate up a bit plant medium stems, up higher again and plant higher stems. Top off.
Running the tank for a few days with nothing in it doesn't actually do anything.
I prettymuch agree with the other comments made. I usually set the substrate and put 6-8" of water and then start planting. taller plants are better placed in deeper water so you can tell what you're doing and keep from tangling the plants all together.
On another note, I just wanted to ask you what kind of substrate and plants you're using? I made the mistake of setting up my first planted venture with a sand substrate and found out later that sand sucks as a plant substrate without fertilizers. My favorite and cheapest setup is to use about 2-3" of the cheapest store brand kitty-litter you can find and then place 2-3" of your favorite gravel on top, then carefully add the water (pouring onto a plate or bowl helps from digging up the litter). Most kitty-litter is made of Clay. I bought mine from wal-mart and it says right on the bag "100% clay". Clay is made of iron, hence the excellent nutrition for the plants. I've heard people freak out over stirring up the kitty-litter into the tank-water. Fish live with clay and soil stirred up in their water all the time in the wild, why would it hurt in your tank? Moral, don't worry about any mess, it'll filter out eventually anyways.
Other popular substrates to put under the gravel are Peat Moss and Topsoil or you can use Laterite or Fluorite as instructed by the bags. Onyx sand is supposed to be "plant friendly" although I don't understand what makes it any good. I used some and didn't notice a difference, I prefer the litter myself. Kyle