I have multiple thin blacks lines on big toe nails, they are at the top of the nails. they only 1mm in length. now i see another line starting on my finger nails. when i google it, it freaks me out. ?

Melanonychia: This is usually a benign condition called melanonychia. Next time you visit your Dr ask him/her to look at it to verify. This is pretty common in people with more melanin in their skin (i.e. Fitzpatrick scale 5-6). If the nails are getting thicker or yellow this could also be due to a fungal infection (onychomycoses). Neither of these conditions are dangerous, but the latter should be treated.