Help with playing custom levels.

How do you play them after you add them? when i press "new game" it goes directly to greenflower zone

That's strange...it doesn't do that for me. But if that's happening to you, you could just type DEVMODE in the console and then "skin (name of the character's skin)". Note that the skin name is NOT the same things as the filename.

When you add a level wad the console should tell you what levels were added. If a was that uses MAP01 was added, the game should show in the console:

Added file [insert wad name and number of lumps here]
Loading main config from [insert wad name here]
MAP01

Or something similar. So, you must type:

MAP MAP[Insert map number here] and make sure that there is only once space in between MAP and MAP[Insert map number here].

The same thing applies for all other map numbers.

You could need a maincfg. It is also known as a level header.

MAINCFG and level headers are not the same. But Level Headers are usually stored inside the MAINCFG.

Newbe look if you have this well:

=> The name of your MAP (not the wad, the MAP) is Mapxx (xx is the number of the map. If you wish that your level replace the level Greenflower ACT 1, you should call your MAP01 card.
=> Do you have a header level? More information here: http://wiki.srb2.org/wiki/Level_Header
It should create a file in your wad named MAINCFG through software publishers wad "Slumped" and "XWE"
There are tutorials on SRB2 WIKI who tell you how to use these two programs.

Otherwise, if we had the wad, we can see more easily where the problem and tell you what to adjust.

I have the mystic ruins wad http://mb.srb2.org/showthread.php?t=33879

To show us the problem of your wad, use Sendspace. Go in Sendspace, you click on "Browse" and you chose your wad, then push "Upload file". Then Sendspace give you the link to download your wad, so we can resolve the problem. Copy and paste the link here.

What you have to understand is that there are several different slots that levels can occupy. By default, the game will first go to MAP01, which under normal circumstances is Greenflower Zone Act 1. Many addon WADs replace the first slot, so that you naturally go directly to them. A few others change the slot that the game starts out in. And there are some, like yours, that put the map in a slot other than MAP01 but don't set the game to go to their slot.

To play that level, you have to figure out which slot that level took. You can figure that out in the console...after adding in the WAD, it should show the map number or numbers that have been filled. Let's say that a WAD filled in the slot MAP03. You can go there by typing "MAP MAP03" in the console.