How much SOL do I need to start?

Enough for your trade plus network fees, priority fees and small deposits for new token accounts.

Which tool should a beginner use?

Compare fees and features on the terminals and bots pages. Fees on many are about 1% per trade.

Get a wallet. Phantom, Solflare and others, see the wallets page. Back up your recovery phrase offline and never share it.
Buy SOL. See how to buy SOL in Phantom.
Choose where to trade. A launchpad such as pump.fun, a trading terminal or a Telegram bot. Compare fees there: many charge around 1% per trade.
Set slippage and fees. Too tight a slippage fails, too loose loses value. Read what slippage is.
Check before you buy. Look at holder concentration, dev holding, bundles and whether the mint and freeze authorities are revoked, see the rug checkers page.
Start small. Keep SOL for fees on top of the trade amount.

Read what a memecoin is and what a rug pull is. Most new coins lose nearly all their value. Selling later can be taxable, see the tax tools page.