your example woul be like this
[Serialize]
class myclass
{
fields & methods
}
on your webform
myclass objmyclass=new objmyclass();
set the fields
and now move to session
session["myclass"]=objmyclass;
now whenever you need your object back just use below statement
myclass objsessionclass=session["myclass"] as myclass;
then use any property or method by using this object.
please check object is null or not before using since it might possible session get expired or not set any where.
for seriazable please read http://msdn.microsoft.com/en-us/library/system.serializableattribute.aspx