They are two different titans, the founding is the titan that "works" only with royal blood and basically controls the other titans and eldians (the first titan to ever exist), the attack titan is Erens "original" titan, the first one.
You might be confusing them because Eren has both titans' power. Technically he already had them both since he was 8 yo but we only discovered that further in the story... in the beggining we knew only about the "Attack Titan".
dunno if i made myself clear but like in short they are two different titans
like in appearance. does the founding titan have specific a appearance? i kennot identify (=・ω・=)
welp i dunno if you recall it being a woman like figure
this is basically what it looked like before eren had it: https://vignette.wikia.nocookie.net/shingekinokyojin/images/5/5c/Founding_Titan_character_image_%28Ymir_Fritz%29.png/revision/latest/scale-to-width-down/350?cb=20180303212428
OR THIS:
https://vignette.wikia.nocookie.net/shingekinokyojin/images/3/3b/Founding_Titan_character_image_%28Frieda_Reiss%29.png/revision/latest?cb=20190428002418
(Two different people in both pictures, the first was the original founding titan and the second person was from the royal family)
No titan really has a specific appearance (this chapter proved just that) as a general rule it kinda looks like the user's human form.
yea yea thankies. i just found outs Eren, having and using the founding titan. He looks weird, inverted and looks like some insect alien. hahaha
Someone explain to me what is the difference between Founding Titan and Attack Titan? I'm Confused :(