Daisies are a broad leaved weed with small, white flowers with yellow centers. These need to be spot treated with a weed killer. Regular mowing will prevent them from spreading. Crabgrass is a grassy weed, it has long stems with nodes from central rosette. General weed killer can be applied.
Wild onion is a grassy weed, it has long , straight stems and grows in clusters with a strong odor.
You will need to remove these by hand and treat with a general weed killer. Large areas of weed killer can be applied by using a spreader and powdered weed killer. You will need to pour the desired amount of weed killer in the spreader, and slowly walk across every infected area. When lawn is covered, then water thoroughly. Single weeds can be removed by hand or by spot weeding by using a spray weed killer applied directly on the weed.