On a flat, on a good running Solex 4600 V2,V3 like yours you can just release the brake and roll the throttle hand grip back to start moving. You can pedal to accelerate quicker if you'd like. Uphill you usually have to pedal once or twice around to help it get going.
You can definitely not coast to a stop on a Solex. In fact, you usually need all the brake you can get, and some foot drag action too occasionally, (plus, of course, rolling the throttle hand grip forward on a 4600 V2, V3 like yours). They're not known for their braking ability.