How to build steam in the oven for getting an oven spring?
The most common method of getting steam into the oven during the first five minutes of baking when it is critical for crust formation, at least for a home style oven is:


Place a pan at the bottom of your oven, and pre-heat as well it while pre-heating your oven.  An empty metal loaf pan or even a cast iron skillet would be suitable.  The pan should be metal (ceramic or glass may not fare well with this kind of treatment).
Bring some water to a boil separately, a couple of cups worth.
When you put the loaf into the oven, pour the hot water into the pre-heated pan, which will result in immediate steam production (this is why the pan was preheated, to help it immediately transfer energy to the water, and produce a burst of steam).


In previous questions, you have indicated that you have a toaster oven, not a full sized home oven, at least as we would think of it in the US.  There may not be enough room for this method in such as small oven.

Another method, which may be more suitable to your oven, although possibly less effective:


Obtain a spray mist bottle, such as the kind used for misting plants.  Fill it with clean water.
Preheat your oven thoroughly.
Immediately before putting the loaf in the oven, mist the oven floor and walls.  This will cause a small burst of steam.


The downside of this method is that it only produces a little steam, and it also cools your oven slightly.