For starters, what level are you currently?
Depending on where you are in the leveling process, the advice will be different.

you probably still have to do solo questing while levelling your character and skills.

for easy soloing, use two handed weapon for higher damage (dual wield is higher, but you have to find two weapons not just one). if you need more offense, use medium armor and sharpened weapon. if you need more defense, usr heavy armor and defending weapon. it's better you mix both armor type in 5:2 ratio and eventually max both armor skills.

best attack skill is Biting Jab. it hits AoE but is good for single target too. it's a morph of one of our first skills and we wont gain a better attack after this. at most, you chip in some DoT skills like blood craze from dualwielding or poison injection from bow or rearming trap from fighter guild skill, in between the jabs. but jabs will always be the main attack skill.

you need the first skill from one hand and a shield line as a tank. it taunts enemy and is your only way to hold aggro. you can pull enemies with other skills, but to hold aggro, you must taunt. use the morph that debuff the target's physical resistance and spell resistance.

taunt boss, taunt other hard hitting mobs, hold block when there's an incoming heavy attack, move away from occassional heavy hitting aoe, i think those are the essenetials.

for further debuff: 2nd skill from onehand and shield, heroic slash, can debuff boss's attack by 15% and give you faster ultimate generation. templar's backslash can ve morphed into Power of Light, and further debuff the target's defense. your extended ritual can slow mobs inside them when you have maxed the passive.

for healing, magicka based healing will heal us very little, but it is still good to use Extended Ritual, to remove debuff on yourself, slow enemy, and most importantly give you major mending (+25% healing amount). as stamina templar, you can get good healing from Momentum, last skill in two handed line. morph it into Rally. not sure if the tooltips is confusing to you, i did not understand it correctly when i first read it. it says heal yourself for ~700 per second, and another ~900 when it expires. what it means is: during the 33 second duration, you get 700 health every second, and after the 33 second duration expires, you get 900x33=29700 health. you can recast Rally to get the big heal any time you want, if you recast it after 10sec, you get 900x10=9000 health. (your actual numbers will vary). the best heal for stamina will be Vigor, but you need to play pvp to earn that, so you can just stick with Extended Ritual and Rally at first.

as for buff, jab gives you critical chance buff, rally gives you weapon power buff, rearming trap gives you crit damage buff. rune focus gives you resistance and damage reduction buff.