The sun setting over an Ocean, with land visible in the distance.
On foot, swimming, by Boat, or other usual means of travel
Ocean biomes contain wide expanses of Water, which could have islands scattered throughout. It is not uncommon for Caves and Ravines to exist beneath the surface. It is also possible for part of an ocean to freeze over, if it borders a snowy biome, like the taiga or ice plains.
In the upcoming Update Aquatic, oceans will gain a much more elaborate underwater ecosystem and even some of their own biomes, such as icy ocean biomes which can generate Icebergs. They will also feature Fish Mobs outside of their item form.
Oceans are possibly one of the most inhospitable places in the overworld for players. Masked by the lack of most Mobs, is the risk of drowning. A player can easily drown while attempting to dive deep under water without protection. They could also starve to death while trying to swim large distances across the ocean. In addition, a player may also be attacked by passing guardians or Drowneds. Trees are scarce in ocean biomes; even if a player happens to find an island, they are less likely to find Wood, an essential ingredient in many survival tools.
A deep ocean is one of the worst places for an unsuspecting player to Spawn, because of the depth of the water. A player could suffer or die from drowning damage if they do not consume a potion of waterbreathing, or have a respiration-enchanted helmet.
A boat is the best mode of transportation while traversing this harsh biome, since it increases a player's speed, saving them energy (thus slowing his/her hunger loss), and decreases the chance of getting attacked by guardians. A boat also allows the player to float, without having to use their jump ability.
Oceans are a good place for fishing, since there is nearly no risk of the Fishing Rod digging into any blocks while doing so. fish are some of the main sources of sustenance, and crops can be grown on a hydroponic farm. Pufferfish can be gained easily by fishing in the ocean, and they are the ingredient required for potions of waterbreathing. Both normal, and deep oceans are home to squids, making them a good hunting ground for ink sacs, as long as the player can dive down to grab them safely.
A player can isolate themselves nearly completely from monsters, as long as all surfaces are well lit. The remoteness can also provide isolation from other players.
If a player is aiming to dive underwater to gather sand or clay, or to raid an ocean monument, it would be wise to create potions of waterbreathing, and Armor with the respiration, aqua affinity, or depth strider Enchantments. These potions and enchantments will increase the time players can spend underwater, or help a player mine blocks faster underwater. If a player combines all of these and a potion of night vision, walking underwater is like walking on land.