Here is code and an explanation of how to draw to a screen.
PoseStack matrices = event.getMatrixStack(); // Just get a matrix stack
int x1 = 0, y1 = 0, x2 = 100, y2 = 100; // Cooordinates to draw the texture at
ResourceLocation texture = new ResourceLocation("mod", "path/to/texture.png"); // Texture
RenderSystem.setShaderTexture(0, texture); // Bind texture
Gui.blit(matrices, x1, y1, x1, y1, x2, y2, x2, y2); // Render texture
Hope this helps