1: XP Grinding: you can get XP by playing matches and when you have enough XP you can get rewards from the Season Pass

2: Summoning Units: you can summon a unit for 100 tokens or 10 units for 900 tokens you can get tokens by playing matches and if you are lucky enough you can get good towers rewarded

3: Enchanting Units: to enchant a unit go to the Enchant Units tab select the unit you want to enchant and you can enchant with souls to get souls you can play matches or get them from playtime rewards

4: Join A Clan: to join a clan in Five Nights TD you need to get invited to a clan by a member or by the owner of the clan you want to join or you can create a clan for 1,000 Robux or 10,000 Tokens this is good because you can get rewards if you have enough Clan Rewarded XP to claim them

5: Endless Mode Grinding: to play endless mode in Five Nights TD you need to go behind the entrance behind the Summoning Units tab and enter one of the elevators there and if you are a new player and don't have good experience in the game or many good towers play a lower endless game like endless 1 or 2 and if you survive till wave 100 in at least one endless game match you can get exclusive units from there that can be used

And here are some good towers for starters that didn't decide yet:

Witch Toy Chica

Patriot Freddy

Tarnished Spring Bonnie

Purple Guy

Scott (also known as Animdude)

Hope this helps for beginners bye!