As I said, Amazing Tweed is an effect preset -- it loads Amp Designer settings into the Amp Designer plug-in that you have inserted on the track. The sound of that plug-in will be applied to whatever is playing on the track you have it inserted on. If it's an Audio track and there are audio Regions on the track when you hit Play [Spacebar] you'll hear the audio through the virtual amp & effects; if it's a Software Instrument track, when you play MIDI into the track or record MIDI Regions on the track and hit Play [Spacebar] you'll hear the MIDI data triggering audio from the Instrument through the virtual amp & effects. I'm not sure how else to explain it..

What means an effect preset? An amazing tweed I recorded (and occasionally deleted), was a strange sound on one note. If I checked out on youtube for an amazing tweed, it was normal guitar sound (a man plays it in the guitar). Is that strange one an effect preset? And to get normal sound, you need to use an effect preset with guitar? Without a guitar is just a weird sound - no use.. ? Right?

As I said before, the "Amazing Tweed" preset in GB is an effect -- it will change the tonal balance (adding midrange emphasis) and probably add some distortion to whatever sound is recorded on the track you insert it on; there may be other effects in that preset as well -- an additional distortion pedal effect and a subtle echo effect. Without a guitar or other audio track playing through it there is NO sound -- it's just a collection of processors.

So I understand, amazing tweed is an effect for the sound, it means it's an additive for the real sound (audio, software instrument), right? If I see in youtube a person plays amazing tweed or other presets (are a preset and effect the same by idea?) in a real guitar and it sounds good, so it sounds good because it's a guitar sound what sounds good + an additive gives to the guitar its own benefits? Right?

Yes, that's correct -- an effect simply changes/enhances the sound of the audio/Instrument on whatever track it's used on. A preset is a collection of specific settings for a particular effect -- so for an amp simulator effect (like the Amp Designer effect, which is used in the Amazing Tweed preset), the Amazing Tweed preset is the specific settings of the knobs and the particular amp & cabinet selected. A different preset using that same Amp Designer effect would have different settings.