The heavy of shift comes asking xD

I'm not exactly sure what are you referring to. Just because you are playing via steam or the Gameforge launcher, it doesn't mean you're playing a different game, in the end you're connecting to the very same servers everyone is playing with.

If you're referring to using Gameforge's launcher, you can do that too, download it from their website and copy the game's content into that folder once it's complete. You will also have to ask Support to unlink your Email address from Steam.
If it's not working as intended, you can try to use Gameforge launcher's repair but I strongly advice to seek help from Sun#0314 on Discord, he has a bit more experience in such things than me. x)

If you don't have Discord, you can usually find him in global chat (Mystel like you) as well, just ask around. :3

Quote from Yridrel

Oh, thank you very much, but if I do that, will not I lose any account? I mean, I'll have the Steam account and the Gameforge account together, as I change emails I'll have one or the other xD

yes you will either have the one account or the other. However as stated above, you can link a nonsteam account to your steam account, or link your steam account to an unused email.

If you want to link your steam account to an email, you can go to the website and search around in account management.

If you want to link your nonsteam account to your steam, you will first need to unlink your steam account via support. then on the first startup, the steamlauncher will ask you if you want to link or create an account.

Greetings

Quote from Yridrel

oh, ok, thanks

Thanking him for what exactly? He's misleading you so badly that you could end up losing your entire Steam created account. Just ignore everything he told you except the part about linking a "steam account" to an unused e-mail address which is likely to not mean much to you anyway.

Let's get some things straight first.
There is only 1 type of regular TERA account - one created on the main website. It's permanent and unlinking it from your Steam profile bears no consequences.
There is also a type of temporary TERA account - one created via Steam. Let's call it a guest account, as once unlinked from your Steam profile, it gets deleted and you lose all of your progress.
In difference to a regular account, a guest account doesn't have a real e-mail address associated with it. The only way to identify it as yours is via your Steam ID. So you're given a dummy e-mail address like <your Steam ID>@gameforge.com. When you ask Support to unlink your guest account, they warn you it will get deleted. Why? Because the dummy e-mail address doesn't exist. Should you then create a new account via Steam, it'll use the same dummy e-mail address, so the old account gets deleted first and you can create a new one or link an existing account.

Now that the misinformation has been cleared up, let's see what you're asking and what your real options are.

Quote from Yridrel

yesterday I realized that you can not have the Steam and Gameforge accounts together. Would there be any way to have them? Since, when I started, I played from Gameforge since I did not know Steam. Should it be from another computer or is there some way to play in one?

You should've put more effort into better explaining what you want to ask, starting from the title of the thread. I wasn't even going to open the thread it if I weren't bored at the time.

No, you can't "combine" 2 different accounts into one. You can, however, play them both. In a fair manner, of course - that's what has been confirmed to be acceptable, as you could've seen here:
TERA launcher issues made simple - error messages explained, plus Steam players notes
9:44 Can't log with another account

You can log into both accounts and play both. Since things have changed a little since the creation of this video guide, you have two options:

• As explained in the video, use TERA via Steam to access your Steam created (i.e. guest) account and the normal TERA launcher to access your old (i.e. regular) account. This option requires your to have 2 copies of the game - one to use via Steam and one to use normally;
• What's different now is you can use the normal TERA launcher to access both accounts. For that, you simply need to link your guest account to the main website, thus transforming it into a regular account, so now you'll have 2 regular accounts and you won't even need Steam anymore. You can use the normal TERA launcher to access the account you feel like playing. There is therefore no need whatsoever for you to unlink accounts etc in order to play both acconut because you can only access one account via your Steam profile. Creating a second Steam profile to link to your older account only makes sense if you have disk space issues and are OK relogging between Steam profiles every time you want to switch between your TERA accounts.

How to transform a guest account into a regular one in order to not lose your progress should you wish to unlink the account from your Steam profile is explained here:
Link Steam account to TERA website

Have fun!