This guide will improve over time.
Everything is written here that I myself understood while playing for Sejuani.

You are not a 1v5 champion, and you need to win back from the team, a teleport will help you here. You are obligated to help your teammates to the detriment of yourself. You are 0 3 4, but your teammate is 5 0 3, then your task is done, then just protect him and start fighting, taking all the blow on yourself.

Your strength comes only after the 6th. You will be able to kill most of the characters only after the 6th. And now your forester can come to you and help. Your w helps push the line and put it the way you need it, but don't overdo it. Most likely, you will lag behind the enemy in creeps, but don't worry about it. You are more useful in files than most champions.

+Strong fights
+It's hard to kill under the tower
+W and R have area damage
+Good farm
+Many СС

-There is no way to kill up to LVL 6
-Low mobility
-Low mobility in fights
-Not enough mana to the point of tears

Q:
This ability allows you to dodge jerks or cc effects With skillful useExample: e shen, e gven, e sett...
It can overcome large walls and is a replacement for a flash
It can overcome large walls and is a replacement for a flash
W:
Helps to kill minions.
Has synergy with E
Helps to slow down the enemy and catch up
E:
Helps prevent Champion skill: R malzahar, q Aatrox...
Easily fits with champions by type: sett, Nocturne...
R:
A strong СС skill that allows you to have it with you almost constantly.
A strong SS skill that allows you to have it with you almost constantlyю
Has area damage.
P:
Additional stats allow you to live longer, and the immunity to slow down gives you the ability to chase enemies.

Plated Steelcaps - It is advantageous to collect against a large amount of physical damage or against melee champions.
Mercury's Treads - It is advantageous to collect against a large amount of magic damage or against champions with СС
Bami's Cinder - help push crips and add to the damage
Bramble Vest - Take against hill You can take it at the first back
Anathema's Chains - Buy in rare cases
Abyssal Mask - If your team has 4 ap champions
Warden's Mail - Against physical attacks
Demonic Embrace - The enemy has four tanks
Fimbulwinter - For mana and shields(Collect always)
Force of Nature - Best item against a team with ap damage(The most effective item)
Frozen Heart - The best item against the enemy hell team(The most effective item)
Gargoyle Stoneplate - A good item if you have collected the slots you need and want to add to the survivability in the files (collect the fourth or fifth)
Randuin's Omen - The enemy has a lot of physical crit damage
Spirit Visage - You have a lot of shields in your team (I do not recommend taking them)
Thornmail - Required for purchase if the enemy has a lot of vampirism
Warmog's Armor - Your team likes short fights of 4-9 seconds? Buy with the fourth or fifth slot(Has synergy with Gargoyle Stoneplate)
Frostfire Gauntlet - The best choice in this patch
Sunfire Aegis - Expensive and not cost effective(Collect if you have a good start)