READ THIS: before posting your question, read the lsit to make sure its not on there yet, then make a post about itpost a question here (if its a long or simple question it wont be listed) and hopefully we'll answer it and lsit it for future references.
1. can/how would i make a door open at (amount of time here) minutes into a game?
Trigger_Always -> Target_Delay; Wait = 1500 -> Func_door
1500 is in seconds which is 25:00 minutes added up, change it to whatever you please.
2. how do you make a lift that can connect two different levels of your map together?
That wait key is in seconds, by the way. 1500 seconds is 25 minutes.
As per the lift, I normally use func_trains (I think. I haven't built a lift in ages). I'll
link you to a rather good mapping page, though. Soubok, the creator of Pulse_102, made some nice lifts, and he's got instructions on the page, and due to the magic of html...

3.how would i make a message appear on the screen when (action) happens?
classname target_print
message "ZOMG I'm a message!"
spawnflag 1 send to human team
spawnflag 2 send to alien team
spawnflag 4 send to the player who activated the target_print
4.how do you add textures into Gtkradiant?
If you are using windows then go to C:/Program Files/Tremulous/Base/Textures and create a folder and put you textures in that folder.
5.how would you make water?
create a brush that has a NODRAW shader from you common file, then you texture it with a water looking shader
6.How can i turn off light emiting textures?
By using the texture instead of the shader. Sometimes the shader has the same name as the texture:
you won't be able to select the texture in radiant and the engine will use the shader anyway.
The clean and simple solution is to create a new subdirectory yourmapname in textures/ and copy the textures you use there. Use your own shader file and name your shaders like yourmapname/shadername.
This will usually stop other maps from messing with your textures, and you from messing with
other maps shaders.
Note for the casual reader:
A shader is a script that can use textures (jpeg images, ....) and do interesting things with it
like make it a ladder, nonsolid, or make it emit light.
Use light emiting shaders, seriously. Only add point lights where you want to touch up the lighting.
7.i need to know more about ladders and how they work
http://tremmapping.pbwiki.com/Shader_Ladder8.my map is "leaked" or sv_setbrushmodel: null comes up when i compile

'
Pressing "L" in GTKradiant will bring up a list of entities and brushes. Click on the arrow next to your map name, and look at your entities. Inspect any entities that do not have an arrow on their left. These entities do not have brush origins. Some entities such as path_corner do not need brush origins. Find entities that require brush origins, do not have brush origins, and delete them.
Also be sure you do not have two worldspawn entities.
9.turrets dont show up when i try to make them, whats my issue?
common files put all those things in your base