MemberInfo member = typeof(MyClass).GetMember("membername");
GetMember reference.
If you know type of member you're looking for, you can use .GetMethod, .GetField, .GetProperty, etc.
If you don't know the type you are working with:
var myobject = someobject;
string membername = "somemember";
MemberInfo member = myobject.GetType().GetMember(membername);
Different member types have different means to getting the value. For a property you would do:
var myobject = someobject;
string propertyname = "somemember";
PropertyInfo property = myobject.GetType().GetProperty(membername);
object value = property.GetValue(myobject, null);