Well, poop! That helps -- and it doesn't. Is there a maker's or brand name inside the sound hole or anywhere? I've only been able to find one "lap harp" in that zither/psaltery shape, but without song cards.
Back to square one. Do you have an electronic tuner so you can determine what notes the various strings are tuned to?
I can "teach" you how to play; it's really very simple. Each string is one note of a scale and there are two scales on the instrument -- from the longest string to shortest they should be: do, re, mi, fa, sol, la, ti, do', re', mi', fa', sol', la', ti', do'. Just like that scale we learned in school, or the song from The Sound of Music "Do, a deer, a female deer; re a drop of golden sun..." etc.
We number those strings/notes from 1 to 15 starting with the longest string. Where the electronic tuner comes in is that we want those notes to be accurate, and start with some real world note like a C or G or D. But if you don't have a tuner you can probably just jump right in and see what happens...
Take a simple song like Frere Jacques. You know the tune. So do I, and zillions of other folks. For several reasons, it's a good song to use to start teaching yourself how to play this instrument. It is simple and repetitive.
The tab numbers for Frere Jacques start with the 3rd string from the left and are
Fre-re Jac-que
3-4...5-3
Fre-re Jac-que
3-4...5-3
Dor-mez Vous
5-6...7
Dor-mez Vous
5-6...7
Son-nez les mar-tine-s
7-8...7...6-5-3
Son-nez les mar-tine-s
7-8...7...6-5-3
Ding-ding-dong
3-0-3
Ding-ding-dong
3-0-3