Pick one or two keywords that the entire site should target, and be sure to use those throughout as a common theme. However, every single page of your site should target its own small selection of keywords, and have its own page title, meta tags, and body content.

what do you think would happen if I used the same ones on each page and not different ones?

You would be struggling with the 10,000,000,000 other sites targeting those keywords, and wouldn't rank for many other terms. It's really just very poor SEO practice to not treat every page like an individual page.

so, if i have a website like myspace.com, where people create profiles for themselves, and made my url is: ourspacecom/people-profiles.php, and wherenver someone creates a profile it would make another page like ourspace.com/peopl-profiles.php2345.

and i had 1000 users and have 100 pages that start with ourspace.com/people-profiles.php and i targetd the keywords: personal profiles, people profiles,I would not have a better chance of getting my website found when people search for those keywords?

I am thinking that if i have the same keywords laced throught every people-profiles.php page, and peopel keep making profiles, i will have a whole lot of chances for one of their pages to show up in the search engine when peopel search for the keywords.

is that not the case?

Not necessarily ... you're just giving google a reason to think that every page on your site is just about the same. Why, then, should google take the resources to index every single page of your site? Catching my drift?

i get it.

not to be rude or offensive, but are you hypothesizing or do you know this for a fact? i really want to optimize my website in the best manner possible.

No one knows anything about google's algorithm for a fact, other than the google engineers themselves. Besides, once everyone is ALMOST sure about something, google goes and changes their algorithm to throw us off. However, I'm telling you what I know from experience in running this site in addition to what I have read from other Internet Marketing forums in addition to visiting a lot of search engine marketing and internet advertising trade shows.

so optimizing every page forthe same keywords would be worse than optimizing each page for different keywords. Because if i do the latter then i will have more oportunities to get visitors to come to my site because i am optimizing for more keywords.

for example, if i optimize only for "dodge neon, neon parts," i will only get visitors that are looking for those two keywords, but if i optimize my homepage for that, and my browse page for "dodge performance, neon performance," i now have 4 chances to get visitors to my site, instead of only 2?

Something like that