If you do not have a Second Life account, start here.
If you are already on Second Life, just teleport to a Linden Realms Portal Park (click the link for a list of them to teleport to) and walk through any portal in the sim. You cannot teleport directly into the game, nor can you use landmarks to jump back in. You must walk through a portal. Each portal leads to a different instance of the game, so if you want to play with friends you will all have to use the same numbered portal.The first time you enter the game, and sometimes later on, you may be prompted to participate in the Linden Realms experience. Answer "Yes" to this prompt if you want to enter.
Once you are inside, your game HUD should attach itself automatically. Your "HUD" is a row of five different colored crystals, and a map icon. You do not have to buy one or attach it yourself. If you have used a portal, you should see the HUD. If you do not see the game HUD at the top of your screen, see Troubleshooting the Game HUD .
In the Realm you can find many Rules of the Realms signs, which has a list of the rules that apply after you go through a portal. You are not permitted to fly in the Realm, but you can certainly walk and run. Running is recommended because of creatures like Rock Monsters and other obstacles.
You should already be facing West and you can just walk forward to find the Workshop in the Basecamp. Of course, West is easy to find on your viewer's mini-map, but it's also the only way you can go that isn't full of rocks, trees, and other obstacles.