I don't get any champion shards when I level up. I don't get more than a couple hundred BE or a random emote from most of my levels so far. So how do you buy champions? I can hardly afford a 450 BE champion as it is and even then there's no more of those that I can buy at the time.
Level 1-30 has predetermined rewards for each level, and you get ~ 30,000 BE of champion shards/permanents, and 10,700 BE outright if I'm remembering it right. After 30, every level will get you champion shards that you can disenchant for blue essence.
https://leagueoflegends.fandom.com/wiki/Experience_%28summoner%29
^ this will break down your level up rewards. What Dynikus told about predetermined rewards is accurate, the details are on the wiki if your curious.
You can unlock a lot of champions if you spend your BE wisely early on. Just stock pile till you hit 35.
If your super new i recommend you use each and every Free week champions at last once. if you enjoy them spend a few more games and aim to learn a playstyle and/or Buy some champions who teach basic mechanics.
A example 
helps give players better map awareness because you can try and guess where enemy champion in fog of war are, then on R cast check your guess vs reality. He also needs to have some decent roam and Mp management can be assisted by using blue cards. To do well on him requires some fundamental skills for the game.
When you do eventually get your shards in your champion capsules save up a nice amount because when you get the shards, they are significantly cheaper than slingshotting BE in the store. I got Warwick (ik hes a cheap champion anyway) for 165 BE. So I just save my shards, save up around 10k BE and go Black Friday shopping at the end of each month. And when you get dups of shards, you can dissolve them for BE. Dont forget the daily win mission too. A little BE goes a long way. (Figuratively and maybe literally). My final word to you my sir is.....Demacia [garen-swing]
Not anything helpful, I just really like your account name. For reasons.
you could disenchant one of the champ shards they give you, on my alt I converted cait to BE
https://leagueoflegends.fandom.com/wiki/Experience_(summoner)
Here you go friend
