Iam trying to insert in the table which identity is true and getting the error

Simple: always name your columns.
At the moment you are going:

INSERT INTO MyTable VALUES (1, 2)

which works only if you have two columns in your table and you know the order, because SQL assumes that the values are to be inserted starting with the "left most column" and movign right.
But you don't, you have three columns:

ID    INT, IDENTITY
Ones  INT
Twoes INT

SO SQL is trying to insert the first value you supplied into the "left most column" - ID - and rightly complaining that you can't set the value of an IDENTITY column because that is it's job.
So always add the columns names:

INSERT INTO MyTable (Ones, Twoes) VALUES (1, 2)

Your problem will go away, and future changes to the table won't mess up your data.