T1 shares are those shares that you’ve bought but the delivery of such shares is pending meaning it hasn’t come to your demat account. T2 shares are shares present in your demat account.
The settlement cycle in India is T+2, meaning, if you buy shares on Monday, those share come to your demat account on Wednesday. When the shares hit your demat account, such holdings are shown under T2, till such time that it hits your demat account, shares appear under T1 holdings.