Some of the Photoshop gradient default presets come with transparency / opacity but if you want to add some to your own presets, how do you go about it ? Select the gradient tool and click the editor / presets top left of the control bar (along the top of the application)
The preset editor is now visible. Go to the top of the bar (opacity stops) and click somewhere and at that point a new opacity stop is added. You can also simply select an existing entry. You may see multiple entries already, you can have just a single entry.
You can select and move the marker. As you change the position you will notice that the location field at the bottom of the panel will also be updated. You can set it to 0%, 1%, 50% etc up to 100%. It has to be an integer.
You can delete them by selecting and dragging away from the bar or clicking the delete button at the bottom of the panel (next to location)
You set it to 0% (see through) or 100% (solid) or anything in between via the entry at the bottom of the panel. If you select one with 0% (say) and then click elsewhere, the newly generated entry will also have the same setting of 0% or 50% etc which makes it super easy to add a lot of opacity to your preset in a short amount of time.
You will also notice a little diamond marker between the square markers, they are the midpoints and by default set to 50% so it blends nicely from the left square to the right side square opacity value (so if the left stop is 20% and the right stop if 30% then the midpoint at 50% will give a value of 25%). You can move it, push it closer to lower value will result in a higher opacity for the rest of the range or vica versa. This is more noticeable if you have the stops at 0% and 100% and opacity of 0% and 100%.
Select the tool and set to linear style and click preset picker and set the opacity stop for 20 at 0% and 50 at 100% and 80 at 0% and perhaps set the mid points for each side (the little diamond markers) to be crunched towards the 50% stop. Set the color around the 50 in the middle of the bar. OK. Set to linear. Apply the preset to the art board. You will see a blurry single line, short or long depending on the length applied by the tool. You can apply it again and again to create more and more lines, though how they fade or stay sharp will depend on the tight focus of the midpoints.
You can use the above approach but using the diamond or radial option and you can create a small dab or spot / dot of color and the result will depend on the length applied (the distance from origin and to the release of the mouse). If you have opacity at both ends you will end up with a ring. If you just have the opacity at the far right end, you will end up with a dot. Or if you use a diamond style, a diamond or square depending on the angle.
Many of these different results depend on the styles used such as linear and radial and reflected etc and you can set those with the tool selected via the top control bar
You can also just add 0% and then 100% and then 0% and then 100% etc and have a single color and quickly create a column design that is see-through the bars in the preset. You can apply it in any color as well as adding as many bars as you like (just place them at 1%, 2%, 3% etc). It is a pity there is no automatic feature to do this but it is a manual process. Again, set the style to linear before you apply the columns
You can create the above columns and then add that to an image from left to right across an image in linear mode and then repeat with the same from top to bottom and you will have a basic grid from the presets or perhaps use the opacity and also use different blending modes such as exclusion to create interesting grids. Click preset picker / editor. Go to the opacity bar. Set stop at 0, 10, 20, 30, 40, 50,60, 70, 80, 90, 100.Set the stop at 0 to 0%, set the stop at 10 to 100%, set the stop at 20 to 0% etc so 0, 100, 0, 100, 0, 100 etc. Set the color stops at the 0, 10, 20 etc to different colors. Click OK. Set to linear style. .Apply preset across image. Set blending mode to difference. Apply the preset (the same or modified) across image 90 degrees to the original.
Set the opacity for the far left to 100% and click at 50% and then add a new opacity stop and set the opacity to 0% and then set the far right position stop to 100%. Apply using any colors from left to right with the linear style and then from top to bottom to create a very quick frame. Another option for the frame is to use the preset in linear style and add opacity to the ends of the bar (in the editor) set to 0% and then just add to the four edges of the page and overlap each of the colorful designs to form a quick and easy frame.