C#.net project files

Question

Since I am new to C#.net 2008, I have the following question to ask:
  Since a solution (.sln file) can have several projects in it, can one project file
work with another project file? In other words, can 'object a' in 'project file 1',
work with 'object b' in 'project file 2' by using methods in ''object b' where 'properties
values' are exposed to 'pulbic' access? For example, can object 'manage finances' in 'project
file 1' obtain the 'checking account' values from object 'customer' in 'project file 2'?
 If so, can you tell  me and/or point me to a url that can explain how to accomplish this task?
Is there a possiblity that I need to be concerned with the main method in the program.cs file
for 'project file 2'?