I apogize that my answer is in English, but I hope it is helpful to you.
Second Life is more of a free form simulation rather than a game like World of Warcraft or Halo; all content is actually created by the people playing in it, and depending on what area you visit will dictate what can be done there, based on what the person who 'owns' or 'rents' the area has set up in that area. Some people do indeed set up areas that simulate MMO type games, others set their areas up more for socializing, and yet others for people to explore what they've created, and so forth.
Combat zones have to be set by the owner of the area you are in. There are many areas that you can find if you look up 'gaming' and 'roleplay' regions that are like this and were made for exactly this purpose. However, if you are not in an area that allows combat, you cannot attack other players. Second Life is not really like most online MMO games where you can battle other players directly; not only does the area have to be set to combat mode, but you will also need to buy or be given extras to attach to your character to be able to participate in such activites (the same goes for the sexual activities). None of the effects are permanent; usually you need to give permission for something to affect your avatar in the first place, and disengaging the item that allows you to participate or even just teleporting to a different area is enough to interrupt the action being taken.
There are some players who are good at programming things that can temporarily override your avatar, but usually leaving the area, or, if necessary, logging off for a few minutes can clear those things.
As for the sexual things; if you go into areas designated as 'adult', it is possible to find places that will follow the act all the way through if you participate, but this also needs various attachments and 'HUDs' (avatar controllers) in order to take place. Your best bet is to research various groups before actually taking your avatar to the area to see what is hosted there.
If you want to get a good idea of what you can do in Second life, and where you can do it, a good place to start is on this
page: http://secondlife.com/destinations?lang=en-US
or the Spanish version of 'Destinations'.