Question on SEO for your website?

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If i am selling 5 categories of items on my website lets say i have 5 pages on my site and each one is devoted to selling the following:

1. Scented candles

2. Toy cars.

3. LED lights.

4. Educational Books.

5. Novelty items.

Now if i use SEO and everything else to get my website ranked high in the search engines (without spending a load of money) do i have to specifically choose which category to rank high, eg. when someone types in "scented candles" into google my website is "number 4" on the page due to great amounts of work to get that ranking, however is it still possble that if someone types in "LED lights" into google that i am ranked near lowest for this or does the SEO work i'v done apply evenly accross my website as opposed to specific parts.

Thank you.