Using the various favors of Ubuntu and now the tails operating system.
Get it here:
By far and away tails is the best and easiest I have found.
While I have to take others word that it is secure, the ease of use for it is off the charts
The get started you download the .iso file, and using a free program that lets you install tails to a USB
The most secure but kind of slow is to burn it to a disc, it can not be altered after the fact by malware but it is slower and will give your disc drive a workout.
The other option is to burn it to a USB. Get the fastest USB you can find and buy a name brand from a reputable supplier. The cheap ones are often counterfeit and will work slower that advertised.
Once installed, set the computer to boot from USB or disc drive first.
Boot the machine from the disc or USB and select clandestine mode. This option will load the version below by default.
It looks kind of clunky and the controls are not how you are used to so you can also make it look like this:
It has word processing and a few basic programs installed asides from Firefox.
It also has the added benefit of being near impossible to get malware that will re-load on reboot. If you are on a questionable site, and are worried that you got something installed, simply re-boot.
It runs quite fast once installed and is easy to use. It also will let you visit the dark web.
No web history is saved, nothing will be carried over to the next time you use the machine.
If you are especially paranoid, you can install a computer kill switch that will wipe the ram and burn out the machine with a method described in a future post.