Bhop
Bhop, short for "bunny hopping", is a movement technique that allows you to move faster than normal by jumping and strafing. It is a very important skill to learn in order to get faster times, and is used not only in almost every map, but also in most Source Engine games as a whole. This skill is transferable to games like Counter Strike, Team Fortress 2, and more.
How To
The science behind bhopping in Portal is simple. Jumping allows you to air strafe. When you air strafe, you will gain speed until your next jump. When you continuously jump and strafe at the same time, you will achieve significantly higher speed than just walking. The goal of bhopping is to gain as much speed per jump as possible, and keep your path on course while doing it.
To maintain as much speed as possible, you will want to jump as soon as you hit the ground. You can make this easier by binding your jump key to your mouse wheel. This allows you input jump commands much faster than you would be able to with a keyboard, which lets you input jump many times right as you land, removing the risk of jumping too early. Be careful not to scroll too fast, as this will cause dropped/ignored inputs.
To do this, open the console and type bind mwheelup +jump and bind mwheeldown +jump.
No Strafe
The easiest way to bhop is to not strafe at all. This is often referred to as "w hopping". To do this, just walk forward, jump, and jump again as soon as you hit the ground. This is the easiest way to bhop, but it is also the slowest. Furthermore, it also puts you at a higher risk of accidentally ahopping, which would invalidate a glitchless run. The risk is that you might accidentally turn your mouse too much before your next hop, causing you to ahop.
Single Strafe
The next level of bhopping is to incorporate air strafing, as was mentioned in the "How To" section. Single strafe bhopping is when you strafe only in one direction between jumps. This is typically easier for most players, and it takes a considerable amount of skill to actually gain and maintain speed from double strafing.
To do single strafes, you want to jump, strafe in one direction, then right before you hit the ground, switch strafe direction and scroll jump. If you intend to continue turning in one direction, then don't switch strafe direction after you jump.
Double Strafe
The highest level of bhopping is to double strafe. This is when you strafe in one direction, then strafe in the opposite direction, all within a single jump. This is the fastest way to bhop used by humans, but it is also the most difficult. It takes a lot of practice to get the strafe timing consistent. If done poorly, will be slower than single strafing. This is typically done at a higher level of play, and is not recommended for beginners.
Because of how jumps give you forward speed, it is faster to do one strafe slower, and one snappy strafe right as you land.