Then your misssion is find wood and craft some pickaxes. Before reach to the cave system, while you digging down you will find some coal and iron (that help you craft some torches). After a while you will reach to the cave system, like the images below.
118334 – Rare Ores Under Spawn
In this Minecraft Pocket Edition 0.11.0+ seed you will spawn in a plain biome. After spawn, you should mark the spawn point. Under the spawn is an cave system with a lots of rare ores: diamonds, gold, lapis, redstone…
Seeds : 118334 Work in PE ver0.11.0+