Simple question about loading

So my game is nearly done but i dont have loading map and screen. And when the level opens and Ai starts to spawn there is some lags. Textures are loaded on the go.
The question is if i make loading level and screen it will load all assets or i have to do something extra?

Prefer to do things my self whenever possible for learning material but in case no one answer your post,

I am using this asset from market place Loading Screen System in Blueprints - UE Marketplace

It’s on discount now, just ought to let you know if you got $17 dollars to spare.

I implement the system into my game, the tutorial was easy to follow. It was as simple as populating the dropable blueprint with your maps. Great thing about the BP is that it does seamless loading/streaming. You can pretty much do anything you want in the level transfer map (showing objects like Fall out 4, ping pong game, w/e you want really)

There is also some functions like progress bar

I did tried to follow some tutorial on youtube with loading level but I still have that frozen lag. I guess the answer lies in streaming which I don’t touch since I found the BP

It is nice to pay and get stuff but i want to know what happens and how it happens when you load a level. And how to do it myself.