While the other replies have adequately answered your question, I'd like to give a more nuanced answer, explaining what is good and what is bad about this card and how I would redesign it, all while hopefully explaining the relevant concepts in a way even someone who has never seen an MtG card can follow.

First, the good, starting with the mana cost. This spell costs a single white mana, as indicated by the singular pip to the far right from the name. With white representing law and order among other things, it fits pretty well condition Tom's integrity.

Then there's the type line: Legendary Creature - Human, which is perfectly accurate as far as MtG typing goes. Let me explain: Creature is the card type. It means it's an entity that can do things like attack and block. Human is the creature type, a sub-type of creature, an has no effect besides being a useful hook for other cars effects. Finally, there's Legendary, a super-type that indicates the card represents something unique that you can only have one of in play.

Finally, giving Tom explore is a huge flavour win. There is, however, some terminology that seems obvious to an MtG player that must be understood. First, every card in the game is a spell except land. While you may cast as many spells as you like while you have the mana for it, you may only play one land per turn. You may tap your lands to generate mana of the appropriate colour and unreal it at the start of your turn. Second, +1/+1 counters are simply indicators that a creatures power and toughness - as represented by the numbers at the bottom, 1/1 in this case - is permanently increased by one.

Now for the bad. Let's go back to that Legendary thing; you may have as many grizzly bears as you can summon at the same time, but only one Tom Scott? That's obviously a demerit, and any given Legendary should be designed to compensate for that. This card was clearly not.

Then there is the issue of rarity, as indicated by the icon on the far right of the type line. There are four stages of rarity in MtG: common is indicated by a black icon, uncommon is a silver icon, rare is a mythic icon, and finally mythic rare is a red icon. As the rarity increases, so does the expected impact of the card as well as it's complexity. That card that is the same as this but in green and without Legendary? Common.

Lastly, the things explore does is not actually a part of White's colour identity. Remember how I mentioned that white is the colour of law and order? That's not just flavour, but reflected in the cards you are likely to get in it. Green is the colour that concerns itself with having the largest tracts of land and the biggest, baddest beasties around, though explore is in blue as well, presumably for flavour.

Now how would I redesign this? First of all, I'd change the colour to blue, the colour of curiosity and learning among other things, and increase the mana cost to one blue and one mana of any colour. Second, I'd improve the effect by turning it into "When this card enters the battlefield and every upkeep on your turn, scry 1. Then Tom Scott explores."

So let me explain the terminology I just introduced: The upkeep phase is a part of the turn where nothing happens unless a card says otherwise. It is right after the untap step and right before the draw step. Scry means to look at as many cards as indicated from the top of your deck and put each of them either on the top or the bottom of your deck.

Now, simply by making the effect reoccurring an letting us curate what is being explored, I've not only made Tom Scott more appropriate for a Legendary of his rarity, I've even made the effect more in line with how he has kept a strict schedule and ensured quality all these years, making it both more playable and more flavorful.

I hope that all made sense and that it wasn't too long a read.

Edits: minor corrections

No, probably not. We just got the same card in the latest set, but without being legendary and in green. And while its not bad, it is also not very good. Wouldnt see play in older formats (except in combo decks like Amalia+Wildgrowth Walker) and is currently not seeing much play in Standard.

Probably not, maybe if he explored each turn (rather than once) or had another ability

for 1 mana pretty cool so definitely value but i dont think it should be a legendary creature

I'm in the game any more so idk if theres stuff that does it better currently, but digging for lands for 1 mana is pretty darn good.