I'm editing a tank and I followed transparency for glass tutorial using nodes. I would also like to ask why is my preview different with my rendered? I'm also new to blender so there's probably something wrong Im doing. I've also tried all the tutorial but still shows the same result.
When using glass, it is usually better to use cycles to get a more realistic look. However, there is away to achieve a "cycles glass look" with EEVEE.
First, you can either use a principled shader and set the transmission to 1, or you can use a normal glass shader.
Then, check Screen Space Refraction in the settings dropdown.
In the render tab, check the Screen Space Reflections tab and check Refractions.
You can achieve a quite similar look to glass from cycles using this method.
In EEVEE, I find that glass shaders don't work so well, so I leave them for cycles. For EEVEE, I use this arrangement to get realistic glass - pay attention to the blend modes I have highlighted on the right. If you absolutely must use a glass shader, go with the arrangement I placed above, but generally I find the one I have highlighted (framed) works best. I tinted it blue just to show it better with the fresnel. See image: