someone explain servers to me

I may be really stupid or this could be a problem that everyone has and i just can't find a simple explanation for it but i was recently added to my friends aternos server on minecraft, i've never been in an aternos server or any personal servers, only sponsored ones like the h ive. I logged on for the first time last night while a bunch of people were playing, i started making my house and gathering material but then it got late so i went to bed. but now when i try to log on it says its not pinging, out of date and offline. i just wanna find a nice minecraft girlfriend and settle down on this server but i'm just too much of an idiot. help