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.
If your project will be built on a breadboard, it may be easier to use Stacking Headers. If you just want to stick the boards together and go, female headers are the best choice.
Most of Adafruit's Feather boards ship with the correct sizes of headers. If you need a custom solution, sometimes you need to trim down a female header to fit.
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
Be sure to solder all pins for reliable electrical contact.
(For tips on soldering, be sure to check out our Guide to Excellent Soldering).