There is the gradient tool,which can be found in the toolbar. Select that and then go to the top bar and select the linear gradient style. Select a gradient preset to use such as black to white or green to blue or black to transparency etc
Drag the preset from the top of the document down to the bottom of the document and release, the current preset using the color stops will be generated. The key thing is to hold the SHIFT key down. You don't have to apply the preset across the entire document, you can apply it at 30% down and release the mouse at 60% or apply it from outside of the gradient and across the document and beyond.
You can create a more complex design by using the blending modes of darken or difference again set up in the control bar. Select a preset and and apply from top to bottom or from halfway up to the bottom or from 40% to 50% and the combination of the presets can be infinite
You can quickly create some type and then add a vertical gradient design to that via the layer menu and layer styles and set the overlay to ON and select a preset and then use the linear style and set the angle to 90. You can then also go to the layer menu and layer mask and reveal all and then you will see a thumbnail for the mask appear next to the type. You can now also go to that with your tool and apply any of the presets to that from top to bottom and hold down the shift and depending on the gray scale value of the preset, more or less of the type will be seen. You can then select the type and duplicate the type downwards or upwards to create an interesting overlapping design of your vertical preset with your selected text. If you use a smart object (via the layer menu) the text can also be live and any change to one instance of the designs will be reflected in all the characters added
You can create a single shape, a thin rectangle and set the shape layer to have a fill of preset via the shape fill and set the angle to 90. Go to the layer menu and smart objects and convert to a smart object and then hold down the alt / option to duplicate it and then drag to the side of the original and then flip or rotate the stripe. Repeat this until you fill the document and now you will have an unusual colorful stripes pattern made of the colors in the preset. As it is a smart object, you can always double click the smart object in the layers panel and change the underlying design and all connected to that will also be updated.
You can also store this into an action and create all kinds of combinations and you can always select all the lines and turn that into a smart object and duplicate that and overlay the design and more. You can still alter the underlying gradient and change that to be made up of multiple presets, different blending modes applied to the shape and more. You can also then apply effects to the overall smart object such as liquefy to warp the design etc https://youtu.be/3fY-DA_PUdw