Male headers are the "standard" headers that ship with most boards. They attach to the underside of the board so the plastic spacers are flush with the surface, and the solder joints go on the front of the board.

Female Headers have plastic sockets with short legs coming out one side. They attach to the top side of a board, with the plastic flush with the board and the solder joints underneath, on the back side of the board.

You can then plug a board with male headers into the female sockets and the two boards will be connected.

Stacking Headers are kind of a combination of male and female. They have a socket with long pins coming out. They sit on top of the board with the long pins sticking through the holes. The solder joints go underneath the board, and the long pins can extend down into another stacking header or female socket, or into a breadboard or perf board. As the name implies, you can stack multiple boards one on top of the other with these headers.

Use male headers if you want to build your project into a breadboard - solderless or permanent. They are also used in conjunction with female headers if you want to stack your boards together.

They are standardized in size at 0.1" spacing, with a few exceptions, so in general you can use any header with any microcontroller, FeatherWing, or shield.

Adafruit even stocks them in fancy colors! 

Prepare the header strip:

Cut the strip to length if necessary. It will be easier to solder if you insert it into a breadboard - long pins down

Add the breakout board:

Place the breakout board over the pins so that the short pins poke through the breakout pads

And Solder!

Be sure to solder all pins for reliable electrical contact.

(For tips on soldering, be sure to check out our Guide to Excellent Soldering).

Solder the other strip as well.

You're done! Check your solder joints visually and make sure they all look shiny, and that nothing is bridged.

It's also possible to solder a FeatherWing directly to the other end of these pins if you're looking for the tiniest possible package for your project.

If you want to stack a Feather and FeatherWing, or to attach a LiPoly backpack charger onto an ItsyBitsy or Pro Trinket, female headers make this easy. Use female headers on the bottom board and male headers on the top, and they'll plug right in.

Carefully count out how many pins you need on the female header. Go to the next pin in line and grab it with a pair of pliers and pull it straight out.

Take your flush cutters and snip through the plastic header right through the gap you just made. You may need to file down the edges of the header for neatness, but often these cutters give a pretty beautiful cut.

Tape In Place

For sockets you'll want to tape them in place so when you flip over the board they don't fall out.

Blu Tack or other removable putty works well also.

Flip & Tack Solder

After flipping over, solder one or two points on each strip, to 'tack' the header in place

And Solder!

Be sure to solder all pins for reliable electrical contact.

(For tips on soldering, be sure to check out our Guide to Excellent Soldering).

You're done! Check your solder joints visually and continue onto the next steps

Place the stacking headers into the board so that the long pins poke through the two rows of breakout pads. Make sure the long pins are sticking out the bottom.

To make it easier to keep these in place, you can use some tape to hold down the two header pieces. Tacky clay also works, whatever you've got handy!

And Solder!

Be sure to solder all pins for reliable electrical contact.

(For tips on soldering, be sure to check out our Guide to Excellent Soldering).

Start by soldering the first row of header.

Now flip around and solder the other row completely.

When you are finished, check that your soldered joints are nice and shiny.

Solder male headers to your topmost board and they will plug right in to the stacking headers, which you can then plug in to another stacking header or into your solderless breadboard.

For headers that are on crooked, it can sometimes help to use the side of your soldering iron to heat all the pins at once, then gently nudge the header so it straightens out while the solder is soft. Be gentle - you can damage your board or break the headers if you push too hard.

To un-solder just one or two pins, you can use solder wick. Solder wick is a braided copper strand that comes in a coil. If you place it next to your solder joint and melt the solder with your soldering iron, the molten solder will soak away from your electronic components and into the wick.

The wick will get saturated with solder, so be sure to move to a clean spot each time you use it.

For more intense jobs (like removing fully soldered headers), upgrade to a solder sucker. This little sucker will vacuum up molten solder and leave your pins and board clean. 

Depress the plunger, then heat up your solder joint until it's molten. Place the head of the solder sucker over the molten pin and press the button. The plunger pops up, sucking the solder with it. Voila! Repeat on all the pins and your headers can be wiggled loose and reattached.