All info in this guide from the the wiki cheat sheet page[wiki.kerbalspaceprogram.com] and in-game tutorial. The goal of this guide is to create a comfortable Steam-based reference page.

If you have some proposition or some parts of the guide still unclear, please let me know in comments, I will fix it.

All important numbers of a stage during design can be accessed by right clicking on it in right-bottom corner.
Example of it:



Delta-V of a spacecraft can be seen in the same place

Red - global Delta-V, the sum of Delta-V of every stage.
Green - local Delta-V, a variable for the particular stage only.

TWR = F(t) / (m * g)

Where:

• F(t) - thrust of the engines
  
• m - total mass of the craft
  
• g - surface gravity

"Thrust to weight ratio" is a ratio of how much your rocket can produce upward force (thrust) to how much mass of your rocket pulling it down (weight). TWR must be above 1 for a rocket to lift off. It's optimal to use TWR between 1.5 and 2 from the launchpad.

I(sp) = F(t) / m

Where

• F(t) - engines thrust
  
• m - fuel consumption in kg per second

ISP is a measure of an engine's efficiency. It may vary in atmosphere and vacuum. For example boosters tend to have higher ISP on sea level, however liquid fuel engines are much more efficient in the vacuum.

Δv = ln(M(s) / M(e)) * ISP * 9.81(m/s^2)

Where:

• ln stands for log base e
  
• M(s) - starting mass of the craft
  
• M(e) - end mass of the same craft
  
• ISP - specific impulse of the engine

Basically Delta-V is your speed after burning all the fuel. It's very important number since it allows to understand how effective specific design and if the rocket able to reach destination.

There exist various Delta-V maps and tools of the Kerbol system. One of the best is "https://ksp-visual-calculator.blaarkies.com/dv-planner" because it allows to set up checkpoints on a mission.

Source[github.com]

Other sources where you can learn more:

• In-game tutorial
  
  
• "Tutorial[wiki.kerbalspaceprogram.com]" page on the wiki
  
  
• YouTube series of tutorials by Scott Manley
  
  
• There is few very useful guides with a lot of information. As much as I want to copy and paste borrow some stuff, the content of guides extend far beyond simple cheat sheet.
  MATH by MAD
  Kerbal Physics by RÉEEEEEPörTéD