The wallet restore height is a setting that tells your wallet software at which block height it should start scanning the blockchain looking for transactions. Ideally it should be the number of the block which included the first incoming transaction to your wallet.
If you set a restore height higher than the block height of your first incoming transaction, your wallet software will not detect all transactions of your wallet. In consequence, your balance will be wrong and your wallet software will not work properly.
If you set a restore height lower than the block height of your first incoming transaction, your wallet software will scan unnecessary blocks. In consequence, your initial wallet synchronization will take longer than necessary, but your wallet software will still work.
Therefore, if you're unsure about the block height of your first incoming transaction, it's always better to set a lower restore height instead of a higher one.
On the next field, type your 25 word `mnemonic seed`. It is expected that some mnemonic seeds have repeated words, as they work as a verification for errors (checksum).
Use the field `Seed offset passphrase` to enter your passphrase, if you have one. When you enter a passphrase, Monero GUI will use your mnemonic seed together with your passphrase to compute a new wallet.
The next field allows you to enter a `Restore height`. Even though this field is optional, it's not recommended to leave it blank, since setting a restore height makes your wallet synchronization faster. Ideally it should be the number of the block which included the first incoming transaction to your wallet: