This next step is the hardest. (It's why Step 2 needs to be learnt well - so they can give all their attention to this step).
Making shoelace loops needs lots of finger and hand coordination. Your child needs good coordination to make the first loop. They need even better coordination to make the second loop. This is because when learning your child can use two hands to make the first loop. But they can only use one hand to make the second one. This is because one hand needs to hold the other loop in place while the second one is being made.
When children are learning this stage it's best to have them make the first loop in their "non-dominant" hand (e.g. if they are right handed make it in their left hand). This is because their coordination in their non-dominant hand won't be as good. Using two hands will make it easier while they learn. They can then make the second and harder loop in their dominant hand with it's better coordination. Once they get the hang of doing this they can then learn to make each loop with one hand in the same way adults do up their laces. But it might take a while to reach this stage.
Tying these loops together is hard in two ways. They need to make the same pattern they made in step 2 (another reason why that step is important). But they need to hold onto the loops so they don't slip out of their hands at the same time. This might seem easy but it's hard for a child. To help them make sure you show them the steps very slowly (the slower and more precise you can show your child the easier they will find it). It might take a lot of practice before your child can do this complicated step easily but practice helps.