To start with, C# is case sensitive, so
SavingAccount aSavingAccount;
Is not the same class as
List<savingaccount> accounts = new List<savingaccount>();
And since they are different classes, the latter can';t contain instances of the former! Plus, one is probably wrong so the compiler is probably telling you "I can't find class XXX".
The "Red Lines" are telling "there is a problem with this code" - if you look at the Errors pane it will give you a text description of what the problem is. (Double click the error message, and it'll take you direct to the line in error.)