1. Pencil tool– There are several techniques to draw precisely, some of which being

• SHIFT- hold this down for a line tool
• scrollbar+eraser: if you want to make a box or circle of some kind of material, you can scroll the brush up to a large size (hold SHIFT to change how wide the brush is), scroll down by 2 and clear all the material inside this.
• TAB changes the brush shape
• time: if you're talking about art saves, a lot of people just go through and place elements, pixel-by-pixel. It's extremely tedious, but the end results are impressive.
• 
  
• stamps: rotate stamps with R, mirror stamps with SHIFT+CTRL+R. Very useful for repetitive borders etc.

2. The Wiki on this site is probably the closest thing, but even then there are gaps in it. If in doubt, just fiddle around with variables like 'tmp' and 'tmp2' using the PROP tool, and see what it does. (Protip: DEUT life 999999999 + PROT = apocalypse)

3. PUMP is very useful, but DEUT/PLUT + NEUT works to start it up as well. Note that pressure is NOT saved with a simulation.

4. Depends hugely on which elements. Some powders are less dense than others (e.g. CLST is lighter than BRMT), as are liquids (i.e. OIL on WATR) but on the whole, it's easiest and most relaible to use STOR with its ctype set to whatever you want to copy.

BTW, putting a tilde (~) in front of a number will turn it into an embedded save. To stop it doing that, just put a space between the tilde and the numbers.
e.g.

@Tjakka5 (View Post)

1- the pincel tool is your mouse (right click to draw the selected element with the cyan color) (left click to draw the selected element with the red color) (mouse wheel to set the brush size or press it to select the element the the mouse is on it) hold ctrl and left click to scale a square, hold shift and left click to make a line(you should move your mouse) press ctrl + shift + lift click/right click to fill the area with the element thet you selected with red or cyan square. press tab to change the brush size.

2- There is in the wiki https://powdertoy.co.uk/Wiki/W/Main_Page.html

3- I didn't understand but I have got two things to tell you related to what you said. 1- URAN get a high temperature when it gets a high pressure and BOYL throw a high pressure to the air when it gets a high temperature.

4- you can do that with a pixel of STOR and PIPE next to it. change the ctype of STOR to whatever you want it to only take that element then cover everything around. This is @greymatter 's design

1. The only foolproof way to draw elements exactly is to press 'Z' to zoom in. The zoom can be adjusted with your mouse wheel. 

2. 'On one page' Not really. The best you can do at the moment is to go on the Wiki.

3. Aironly wall.

4. Use STOR with a ctype of the element you want to filter.

2 yes there is,