The 534 is a four ball siteswap
pattern which combines three different throws (a high Cascade throw, a low
Cascade throw, and a Fountain throw) to bring a more dynamic twist to the
standard tower siteswaps (531, 7531, etc.)
To learn the 534, start with two balls in your dominant hand and one ball in your non-dominant. Make a high Cascade throw from your dominant hand, and then immediately follow it up with a low Cascade throw from your non-dominant hand (as if juggling the first two throws of the 531). As that low Cascade throw is in the air, make a vertical throw from your dominant hand, clearing space for you to catch that low throw. Then catch the first throw with your non-dominant hand (it is important to make sure that this high throw is caught after the low second throw is caught). Finally, catch the vertical throw with your dominant hand.
Practice this extensively on both sides. To add in the fourth ball, you are going to make another high Cascade throw from your non-dominant hand after you make the vertical throw from your dominant hand. This will clear space for you to catch the first high Cascade throw, which was thrown at the very beginning from your dominant hand.
As shown, practice this on both sides. As you may have noticed, the last throw shown in the animation above is a mirror image of the first throw you made. This means that the cycle simply repeats again, this time using the opposite hands for each throw. To run the full 534, just keep repeating the cycle. This is however easier said than done, since the 534 requires precise timing that will take many days if not weeks of practice to master.