I don't now how to go about this. I'm trying to print to Nations Photo Lab. They say I need to have a bleed & trim that should measure 3.75 x 2.25 and the trimming area, where the card gets cut, is 3.5 x 2 and the safe zone where you want to keep all the important info like text is 3.25 x 1.75. I'm working in Lightroom. My template that I'm using is a 5x7. When it prints it's a bit on the small size because I guess it's used for web. All I want is to print a 5x7 post card with a collage of photos on it. It has a grey border as well, so I can't have any white paper showing. Right now I am just guessing on how much space I need around the edge. I can't have cut lines on because I have a collage of photos and can't have lines going though it. Please help!
It looks like you're getting the wrong dimensions for what you want. Business cards are commonly found in a 3.5"x2" size. 3.5"x2" is the target size to cut.
To ensure that text isn't trimmed off if the cuts are made too short it is suggested that they are 1/8" inch inside the edges (which is your 3.25"x1.75" safe zone; 1/8" on each side).
On the other hand, if the cuts are made too large then there will be unprinted (usually white) strips on the edges, so it's recommended to bleed over some extra background in case that happens.
This all applies to your 5"x7" postcards as well, but with different dimensions. If it's the same 1/8" tolerance then you'd have a 4.75"x6.75" safe zone and a 5.25"x7.25" bleed. To mock this up in your editor of choice you'd make a 5.25"x7.25" canvas and place guides 1/8" inside the edges to mark your target cut line, then another guide 1/8" inside that to mark your safe zone.
Also, it's not a good idea to do borders because if the cuts don't come out even (and they probably won't, just a fact of life when working with this type of equipment) then it'll appear off as one side will be thicker or straighter than the others.