You know, I think you should study properly. All these questions are answered in every course in Chinese. 到 added to a verb = successful carrying out of whatever verb it was added to 做到 = successful carrying out of doing 做不到 = unsuccessful carrying out of the doing 找到 = successful carrying out of the search, i.e find 找不到 = couldn't find It is very often used in the negative, 做不到, form. 到, by itself = arrive (makes a lot of sense, huh) I have gone = 我走了 Completion is indicated by the marker, 了. Now that's enough for now. Keep on learning.

in '我做/我做到' the verbal is 做, '到' is for PF. in 我到了 , the verbal is '到'， 了 is for PF. I have gone = 我走了

its ok . 我做(it is not a completed sentence, it should be add a noun after it.such as "我做作业") 我做到（the same to the first one. example,我做到一半。means i have done half of the job or something like this ） 我做到了（it means i have made it or been successful ） 我到了（it means"i have arrived ." on this case,到 is a verb.and in common you suppose to add a place after it. such as 我到你家门口了。）