Lumifer's answered this already in a sibling comment, but note that this general class of question is answered in the Procedural Knowledge Gaps thread (or its repeat). (I wrote a longer answer to this particular question there.)
5Lumifer
You decide on which fund you want, open an account with the appropriate mutual fund company (e.g. Vanguard) or a brokerage, transfer to them the money from your checking account, and put that money into the fund.
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