To send SOL, you will need to interact with the SystemProgram.
import {
Connection,
Keypair,
SystemProgram,
LAMPORTS_PER_SOL,
Transaction,
sendAndConfirmTransaction,
} from "@solana/web3.js";
const fromKeypair = Keypair.generate();
const toKeypair = Keypair.generate();
const connection = new Connection("https://api.devnet.solana.com", "confirmed");
const airdropSignature = await connection.requestAirdrop(
fromKeypair.publicKey,
LAMPORTS_PER_SOL,
);
await connection.confirmTransaction(airdropSignature);
const lamportsToSend = 1_000_000;
const transferTransaction = new Transaction().add(
SystemProgram.transfer({
fromPubkey: fromKeypair.publicKey,
toPubkey: toKeypair.publicKey,
lamports: lamportsToSend,
}),
);
await sendAndConfirmTransaction(connection, transferTransaction, [fromKeypair]);