In CSS Grid Layout, grid items refer to the elements that are placed within the grid container. These items can be any valid HTML elements. To place grid items within the grid, we have different techniques available.

One of the main techniques is using the grid-row and grid-column properties to specify the starting and ending lines of the grid cells that the item occupies. For example, setting grid-row: 1 / 3 will make the item span two rows, starting from the first grid line and ending on the third grid line.

Another technique is using the grid-area property to assign a name to a grid item and then using that name within the grid-template-areas property of the grid container. This allows us to create layout patterns and assign items to specific areas.

Lastly, to control the position of grid items, we can use alignment properties such as justify-self and align-self, which allow us to align items horizontally and vertically within their grid cells.

With these techniques, we have the flexibility to place grid items wherever we want within the grid container.