There’s no one specific dressing for a venous ulcer, because for this wound the dressing is not the main treatment.
The dressing basics are brief: always keep the wound clean and bandaged to prevent infection; your provider will tell you how often you need to change it; keep the dressing and the skin around it dry; and cleanse the wound thoroughly, following your provider’s instructions, before applying a dressing.
Then comes the thing that matters most about dressings on this wound: you will wear a compression stocking or bandages over the dressing. Your provider will show you how to apply the bandages.
Over the dressing. The compression is the treatment; the dressing goes underneath it. To help treat a venous ulcer, the high pressure in the leg veins needs to be relieved. Compression stockings or bandages worn every day help prevent blood from pooling, reduce swelling, help with healing, and reduce pain.
At a wound care center, dressing choices are general rather than venous-specific: after the wound is clean, a dressing is applied to keep the wound moist, which promotes healing, and to help prevent infection. The types include gels, foams, gauze and films, and a provider may use one or multiple types as a wound heals.
Which of those suits a particular ulcer is a clinical decision. If you have been given a named product, that choice was made by someone who could see the wound.
One instruction worth repeating because it is easy to get wrong under a compression bandage: keep the dressing and the skin around it dry, and try not to get healthy tissue around the wound too wet, because it can soften and cause the wound to get bigger.