The previous guide disappeared along with a banned user so I'm taking the opportunity to compile a more updated version for 2020.
Background
A Score Sender is a program which automatically sends your scores through flash games while waiting a certain time to trick the server into thinking you played the game. It sends the score thereafter, registering that on the server for you to gain neopoints, avatars and trophies without having to actually play the game.
Although there are many score sender programs out there, the safest so far is MAJIN Score Sender, made by j03.
It's a pretty straightforward process. Once you've extracted the .exe file, executive it and go through the motion of installation. I've included the screenshots for you just in case.
Before you start the program, you should check out the Program Settings to make sure everything's in order before starting. Since it's a very sensitive issue that could easily get your account iced if not done properly, you should ensure that everything is in tip top shape before starting.
In box 1, you can make certain changes such as having the bot pause, or ensuring that your account is still logged in before score is sent. It's pretty straightforward and you should work with the bot according to how you are using it to ensure utmost safety.
You may be impatient to start finding Score Sending lists and sending scores, but remember that it's always better to be safe than sorry. MAJIN Score Sender is very safe because the safe timings are updated but you should always do your due diligence to try out the games, have a feel of the timings, know the impossible scores and review scores. One wrong move could mean the end of your account.
If you're thinking of using score sender to earn neopoints... I would suggest for you to find other means such as ABing because score sending for neopoints is sloooow and you don't earn very much. On top of that, it's pretty dangerous compared to using AoB where you're actually playing the game (with major advantages). It's good for getting avatars and trophies (not when the scores are too high).
I hope all these information provided was useful to you, and should you have any questions you may ask here!
If it has to do with technical issues, remember to go to the program section itself and ask! Save your logs at all times and possibly screenshots as well to help the programmers understand your issue and solve your problems!