Once you have a large version of the picture (full screen or full browser window sized) that you want to save for printing, either use the "File" menu to select "Save As" or use your right mouse button to click on the large picture and select "Save Image as" (or similar). Then choose a place to save the picture (the default name is probably OK for you).
If the default picture name you are saving ends with "_l.jpg", then you have a picture that will print very nicely at 4x6 size or possibly OK at a 5x7 size. It WILL NOT print well at 8x10 or larger. If the default picture name you are saving ends with "_vl.jpg", then it will print well at 8x10 or larger (if it is REALLY clear and not grainy when viewed at full resolution on your screen). Even if you are going to print to 5x7 or 4x6, use the "_vl.jpg" version as it will give better sharper prints.
Quality
If you are unsure of the quality available in each of the pictures
you have downloaded, the default file name contains some information
on the quality. Firstly, if you are considering printing a file
that ends with "_l.jpg", remember that the quality is limited to
5x7 at the most for printing, regardless of the quality discussion
below.
If you are printing from the "_vl.jpg" version, then the following quality information is useful (if you have trying to print from the "_s.jpg" version, STOP and go back and get the larger version).
Each picture name contains a "_qxxxx_" portion where the xxxx represents a 4 digit number. The 3rd digit is the print quality indicator (2=poorest, 9=highest) and the 4th digit is the subject pose quality and/or the aspect ratio quality (5=poorest, 9=highest). The 1st 2 digits are the product of the 3rd and 4th digits with an adjustment upwards to allow for grading within categories (9*8=72 but if it is one of the better within that category, it may get a 73, 74, or 75 instead). So, a "_q7598_" in the filename would indicate that it has the top print quality indicator, but the pose or he aspect ratio is not quite at the top level (subject may have a less-than-perfect facial expression or the background my be less desirable or the aspect ratio may cause substantial cropping to occur when printing). If you are making a 4x6 print, you can accept ratings with the 3rd digit as low as 2 or 3, especially if the 4th digit is 8 or 9. If the 3rd digit is high with a low 4th digit, you may still want to print it, but you may want to crop out certain parts of the picture or it may be a humorous picture that causes the pose quality rating to be lower.
Generally, the numerical ranking of the picture should be roughly proportional to the first 2 digits - a "q8199" picture will almost always make a better 8x10 than a "q6488" picture. One of the web pages should show the pictures in descending general quality ranking to make your selection easier (ie. choose the pictures closer to the top of the page).
Cropping
If the picture you save has the exact aspect ratio (height versus width)
as the desired picture size, you are ready to go. Just move the files
to the print shop (by email or on a CD or on some memory media that
they accept) and you should get good prints. If the picture is
taller or wider than the print format you want, the default print
instructions will crop some of the picture off the top and bottom or
from the sides (respectively). You will need to crop the results
in the print shop's system according to the size you want to print.
Good luck - this takes more instructions that are available here!
Enjoy your prints.
Ian Fetterley