Sprites

Select the Entity tool and find env_sprite. Press ALT+Enter and go to Sprite Name. Now press the three dots ... and go to your cstrike/sprites folder and pick the sprite you want. Now look at Scale button the value is 1 change it to 0.5. One last thing left to be done go to Render Mod and select Additive.

Sound

Select the entity tool and create ambient_generic (it is the first entity from the list). Go to object properties ALT+Enter.

Path/filename.wav of WAV - press the three dots ... Now go to your cstrike/sound folder and pick the sound you want.
Volume (10=loudest) - You can change it or leave it default
Start Volume - Set this value from 1 to 10

When you are done with that go to Flags and choose the distance for your sound.

Models

Select the Entity tool and find cycle_sprite. Click with the left and then with the right mouse button on one of the four windows in VHE and press Create Object. Select the entity and press ALT+Enter. New window should appear with the properties of the selected entity. Go to Model/Sprite and press the three dots ... Another window will appear from there go to your cstrike/models folder and choose the entity you want and press Add