DS was diagnosed at 2 (a few months before he turned 3)
His speech initially seemed to be developing typically for a baby in that he gained a lot of words but he stayed at that level for a long time. He had loads and loads of words but no idea what to do with them! I was an SEN teacher before he was born so knew a few things and made him a communication book based loosely on PECS (which I'd been trained in on their two day course when I was teaching). We'd also been signing with him since birth which he understood but didn't really use himself that much.
His book had loads of symbols of food, toys, photos of people in his life, places, 'help' type symbols (feeling poorly, somethings hurting, something's too noisy or too sticky etc). Then I'd give him opportunities to communicate basically so rather than him screaming and me realising he probably wanted a snack I'd get him to use his book to show me what food he wanted and model the language he needed to use.
Also lots and lots of play commenting on what he was doing without asking questions-this is really tricky to do because it's our natural instinct to extend play by asking questions! Loads of reading together as well, commenting on what I was doing, basically narrating our lives!
After a while his speech extended to copying scenes from favourite films and tv programmes in his play (Lightening McQueen featured heavily!) To an outsider it looked like he was talking loads but if you know the film then you know it's lifted verbatim from the script.
Eventually he started putting together his own little phrases, these got extended more as he started to understand more what he was supposed to do with words and this was enhanced by his speech therapy (that he'd started receiving by this point along with his diagnosis and subsequent EHCP) focusing on something called Shape Coding, where each part of a sentence is written down in an assigned shape eg verb is always a triangle, noun is always in a circle etc (I hated this because I'd used a similar system when teaching but it was with colours and I kept wanting to do this instead because the colours were automatic for me!)
He's now 8 and chats away and his therapy focuses more on the social aspects of conversation and the 'give and take' of listening and responding. He has a very quaint turn of phrase sometimes which is adorable.
Your child is still very very little. At the moment just focus on the quality interactions and play and narrating what you're doing. With the assessment will come support hopefully and they will come up with the best plan for his individual needs.
Even if your child doesn't 'talk' with words, speech therapists are wonderful people and they will find a way for your son to 'talk' to you using a communication method that will be just as clear. You will be able to understand him and what he needs and feels. He obviously gets the point of communicating (taking you by the hand and leading you somewhere is communicating and 'talking' to you in his own way right now) so that's really positive!