To be able to enter the material in the stock by means of delivery notes or purchase invoices, we will go to:

Finance → Purchases and suppliers → Delivery notes.

We will see a window with some already created, but we will click on the "New" button as shown in the image.

We will open the tab of the purchase receipt, where we fill in with all the data, the supplier, the document number, etc.
But the most important thing here is the "Article" part at the bottom of the screen, where we click on the "New" button to enter new articles.

We will open the next window, where in reference, we will open a drop-down, where we will select the reference we want and we will see how the other information is filled, except the "Price U" that we must enter the price we want and press to update:

We will click on the "Insert" button in the previous window and we will have already introduced material in stock using a delivery note.