I have been a long-time Slacker. Slackware is the all-in-one operating system created by Patrick Volkerding. It is unlike any other OS out there because it literally has 9 gigabytes of software contained in the installation disks of the system. It is also one of the most stable operating systems out there because the Pat is a very particular gatekeeper. As a result, the software is not as up-to-date as some other operating systems.
In the most classy way ever, you will find Slack at http://slackware.com under the link that says Get Slack. As the great J.R. "Bob" Dobbs himself once said, "You gotta get that slack in your life!" Go ahead and click through to get yourself some slack.
One of the longtime favorite pieces of software for writing ISOs to USB drives is called Unetbootin. Once you get this installed, it is pretty straightforward how to write the ISO you downloaded and verified to the USB stick.
Once it's written, it's time to reboot. Now depending on the make and model of your computer there may be a different key during reboot to get to the BIOS. We need to get to the BIOS so that our computer will allow us to change the Operating System that is loaded at boot time. This is also pretty simple. Usually it is the
<Delete> key that gets you to the BIOS menu, but some computers do things a little differently. So consult DuckDuckGo again for your specific computer if
<Delete> does not work.
Once in the BIOS, it's time to select the USB drive to boot from. It's usually in a section labelled
<BOOT> or something to that effect. You should find the name of your USB drive there. Mine is often a PNY Flash or something of that nature. You'll want to boot from it and wait for Slackware to load.
The first screen you come to will be a TTY interface. Just read the text carefully and you'll know what you need to do. If you don't know, DuckDuckGo is your best friend. I don't plan on going much further into depth on this, as there are a lot of better guides out there, including the official channel at Slackware: Installation Help.
Once installed, Slackware already has everything you generally need ready to use. If you ever need any help figuring things out with Slackware, there is a relatively vibrant community. Below are a couple of links to some great community-built resources.
Here is where you will find answers to a lot of questions about specific pieces of software included with Slackware.
This is a forum where you can usually find answers to issues or questions you have about Slackware.
This is a fantastic resouce built by Klaatu from GNU World Order to help you get up and on your feet for just about any creative project that you might have.
And that's it! Slackware is one of the mainstays of the Free Software community, and most users will find it fairly simple to operate. If Slackware still seems like a bit of a challenge, however, don't worry and head on over to check out elementaryOS.